JEE Ellipse Questions

The centre of the circle $$x^{2}+y^{2}-2x-4y-11=0$$ is obtained by completing the squares.
$$x^{2}-2x+1+y^{2}-4y+4=11+1+4$$
$$\Rightarrow (x-1)^{2}+(y-2)^{2}=16$$

Hence the centre is $$C(1,2)$$ and the radius is $$r=4$$.

The ellipse is $$3x^{2}+py^{2}=4$$ and it passes through the point $$C(1,2)$$, so

$$3(1)^{2}+p(2)^{2}=4$$
$$\Rightarrow 3+4p=4$$
$$\Rightarrow 4p=1 \;\Longrightarrow\; p=\frac14$$

Therefore the ellipse is $$3x^{2}+\frac14\,y^{2}=4$$.

Divide by $$4$$ to get the standard form:

$$\frac{3}{4}x^{2}+\frac{1}{16}y^{2}=1$$
$$\Rightarrow \frac{x^{2}}{\frac{4}{3}}+\frac{y^{2}}{16}=1$$

Comparing with $$\frac{x^{2}}{b^{2}}+\frac{y^{2}}{a^{2}}=1$$ (major axis along $$y$$-axis), we have

$$a^{2}=16,\;a=4,\qquad b^{2}=\frac{4}{3}$$

The focal length satisfies $$c^{2}=a^{2}-b^{2}$$, hence

$$c^{2}=16-\frac{4}{3}=\frac{48-4}{3}=\frac{44}{3},\qquad c=\sqrt{\frac{44}{3}}$$

The foci are $$F_{1}(0,c)$$ and $$F_{2}(0,-c)$$.

Let the focal distances of the point $$C(1,2)$$ be $$f_{1}=CF_{1}$$ and $$f_{2}=CF_{2}$$.

Since $$C$$ lies on the ellipse, the sum of its focal distances equals the major axis length:

$$f_{1}+f_{2}=2a=8 \quad -(1)$$

Now compute the squares of the distances.

$$f_{1}^{2}=(1-0)^{2}+(2-c)^{2}=1+(2-c)^{2} =1+4-4c+c^{2}=5-4c+c^{2}$$
$$f_{2}^{2}=(1-0)^{2}+(2+c)^{2}=1+(2+c)^{2} =1+4+4c+c^{2}=5+4c+c^{2}$$

Adding:

$$f_{1}^{2}+f_{2}^{2}=(5-4c+c^{2})+(5+4c+c^{2}) =10+2c^{2} \quad -(2)$$

From identities,

$$(f_{1}+f_{2})^{2}=f_{1}^{2}+f_{2}^{2}+2f_{1}f_{2} \quad -(3)$$

Substitute $$-(1)$$ and $$-(2)$$ into $$-(3)$$:

$$8^{2}=10+2c^{2}+2f_{1}f_{2}$$
$$64=10+2\left(\frac{44}{3}\right)+2f_{1}f_{2}$$
$$64=10+\frac{88}{3}+2f_{1}f_{2}$$
$$64=\frac{30}{3}+\frac{88}{3}+2f_{1}f_{2} =\frac{118}{3}+2f_{1}f_{2}$$

$$\Rightarrow 2f_{1}f_{2}=64-\frac{118}{3} =\frac{192-118}{3}=\frac{74}{3}$$

$$\therefore\; f_{1}f_{2}=\frac{37}{3}$$

Finally,

$$6f_{1}f_{2}-r=6\left(\frac{37}{3}\right)-4 =2\cdot37-4 =74-4 =70$$

Hence $$6f_{1}f_{2}-r=70$$, which matches Option C.

We have two ellipses with the same eccentricity $$e = \frac{1}{\sqrt{3}}$$, product of latus rectum lengths $$= \frac{32}{\sqrt{3}}$$, and distance between foci of $$E_1$$ is 4.

For the ellipse $$E_1$$ given by $$\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$ with $$a \gt b$$ and eccentricity $$e = \frac{1}{\sqrt{3}}$$, the distance between the foci equals $$2ae = 4$$, so $$ae = 2$$, yielding $$a = 2\sqrt{3}$$. Then

$$b^2 = a^2(1 - e^2) = 12\left(1 - \frac{1}{3}\right) = 12 \times \frac{2}{3} = 8$$

and hence $$b = 2\sqrt{2}$$. The latus rectum of $$E_1$$ is

$$\ell_1 = \frac{2b^2}{a} = \frac{16}{2\sqrt{3}} = \frac{8}{\sqrt{3}}.$$

For the ellipse $$E_2$$ defined by $$\frac{x^2}{A^2} + \frac{y^2}{B^2} = 1$$ with $$A \lt B$$ (so the major axis is along the y-axis) and the same eccentricity $$e = \frac{1}{\sqrt{3}}$$, we have

$$A^2 = B^2(1 - e^2) = \frac{2B^2}{3}.$$

Its latus rectum is

$$\ell_2 = \frac{2A^2}{B} = \frac{2 \cdot \frac{2B^2}{3}}{B} = \frac{4B}{3}.$$

Since the product of the latus recta is

$$\ell_1 \cdot \ell_2 = \frac{8}{\sqrt{3}} \cdot \frac{4B}{3} = \frac{32B}{3\sqrt{3}} = \frac{32}{\sqrt{3}},$$

it follows that $$B = 3$$ and hence

$$A^2 = \frac{2 \times 9}{3} = 6.$$

The equations of the ellipses become

$$E_1: \frac{x^2}{12} + \frac{y^2}{8} = 1,\qquad E_2: \frac{x^2}{6} + \frac{y^2}{9} = 1.$$

From the first,

$$x^2 = 12\left(1 - \frac{y^2}{8}\right) = 12 - \frac{3y^2}{2},$$

which substituted into the second gives

$$\frac{12 - \frac{3y^2}{2}}{6} + \frac{y^2}{9} = 1$$

$$2 - \frac{y^2}{4} + \frac{y^2}{9} = 1$$

$$y^2\left(\frac{1}{9} - \frac{1}{4}\right) = -1$$

$$y^2 \times \left(\frac{-5}{36}\right) = -1 \implies y^2 = \frac{36}{5},$$

$$x^2 = 12 - \frac{3}{2} \times \frac{36}{5} = 12 - \frac{54}{5} = \frac{6}{5}.$$

Thus the four intersection points are

$$\left(\pm\sqrt{\frac{6}{5}},\; \pm\sqrt{\frac{36}{5}}\right),$$

forming a rectangle by symmetry. Its side lengths are $$2\sqrt{\frac{6}{5}}$$ and $$2\sqrt{\frac{36}{5}}$$, so the area is

$$2\sqrt{\frac{6}{5}} \times 2\sqrt{\frac{36}{5}} = 4\sqrt{\frac{216}{25}} = 4 \times \frac{6\sqrt{6}}{5} = \frac{24\sqrt{6}}{5}.$$

The correct answer is Option 4: $$\frac{24\sqrt{6}}{5}$$.

The standard equation of an ellipse with its major axis along the $$x$$-axis is $$\frac{x^2}{a^2}+\frac{y^2}{b^2}=1$$, where $$a \gt b \gt 0$$ and its eccentricity is $$e$$.

1. Length of the latus-rectum (the chord through a focus perpendicular to the major axis) is
$$\text{Latus rectum}= \frac{2b^{2}}{a}$$.

2. The eccentricity and the semi-axes satisfy the relation
$$b^{2}=a^{2}(1-e^{2})$$ $$-(1)$$.

3. We are given that the length of the latus-rectum equals $$10$$:
$$\frac{2b^{2}}{a}=10$$ $$-(2)$$.

4. The eccentricity $$e$$ is the minimum value of the quadratic function
$$f(t)=t^{2}+t+\frac{11}{12},\; t\in\mathbb{R}$$.

The minimum of a quadratic $$At^{2}+Bt+C$$ with $$A\gt 0$$ occurs at $$t=-\frac{B}{2A}$$.
Here $$A=1,\; B=1,\; C=\frac{11}{12}$$, so the minimising value of $$t$$ is
$$t=-\frac{1}{2}$$.

Substituting back gives the minimum value (and hence the eccentricity):
$$e=f\!\left(-\frac{1}{2}\right) =\left(-\frac{1}{2}\right)^{2} +\left(-\frac{1}{2}\right) +\frac{11}{12} =\frac{1}{4}-\frac{1}{2}+\frac{11}{12}$$
$$=\frac{1}{4}-\frac{2}{4}+\frac{11}{12} =-\frac{1}{4}+\frac{11}{12} =\frac{-3}{12}+\frac{11}{12} =\frac{8}{12} =\frac{2}{3}$$.

Thus $$e=\frac{2}{3}$$ and $$e^{2}=\frac{4}{9}$$.

5. Using equation $$(1)$$:
$$b^{2}=a^{2}\!\left(1-\frac{4}{9}\right)=a^{2}\!\left(\frac{5}{9}\right) =\frac{5a^{2}}{9}$$ $$-(3)$$.

6. Insert $$(3)$$ into the latus-rectum condition $$(2)$$:
$$\frac{2}{a}\left(\frac{5a^{2}}{9}\right)=10 \;\;\Longrightarrow\;\; \frac{10a}{9}=10 \;\;\Longrightarrow\;\; a=\frac{10\times9}{10}=9$$.

Therefore $$a^{2}=9^{2}=81$$.

7. Find $$b^{2}$$ from $$(3)$$:
$$b^{2}=\frac{5a^{2}}{9} =\frac{5\times81}{9}=5\times9=45$$.

8. Finally,
$$a^{2}+b^{2}=81+45=126$$.

Hence $$a^{2}+b^{2}=126$$. The correct option is Option B.

For the ellipse $$\frac{x^2}{9} + \frac{y^2}{4} = 1$$, the equation of the chord with midpoint $$(h, k)$$ is given by:

$$ \frac{xh}{9} + \frac{yk}{4} = \frac{h^2}{9} + \frac{k^2}{4} $$

Given midpoint $$\left(\frac{5}{2}, \frac{1}{2}\right)$$:

$$ \frac{x \cdot \frac{5}{2}}{9} + \frac{y \cdot \frac{1}{2}}{4} = \frac{\left(\frac{5}{2}\right)^2}{9} + \frac{\left(\frac{1}{2}\right)^2}{4} $$

$$ \frac{5x}{18} + \frac{y}{8} = \frac{25}{36} + \frac{1}{16} $$

RHS: $$\frac{25}{36} + \frac{1}{16} = \frac{400 + 36}{576} = \frac{436}{576} = \frac{109}{144}$$

LHS: $$\frac{5x}{18} + \frac{y}{8}$$

Multiplying through by 144:

$$ 40x + 18y = 109 $$

Comparing with $$\alpha x + \beta y = 109$$:

$$\alpha = 40, \quad \beta = 18$$

$$\alpha + \beta = 40 + 18 = 58$$

The correct answer is Option 1: 58.

The given ellipse is $$\dfrac{x^{2}}{4^{2}}+\dfrac{y^{2}}{3^{2}}=1$$, that is $$\dfrac{x^{2}}{16}+\dfrac{y^{2}}{9}=1$$.

Case 1: Find the values of $$p$$ for which the line $$y = x + p$$ is tangent to the ellipse.

Substitute $$y = x + p$$ in the ellipse:

$$\dfrac{x^{2}}{16} + \dfrac{(x+p)^{2}}{9} = 1$$

Multiply by $$144$$ (the LCM of $$16$$ and $$9$$):
$$9x^{2} + 16(x+p)^{2} = 144$$

Expand the square:
$$9x^{2} + 16\bigl(x^{2}+2px+p^{2}\bigr) - 144 = 0$$

Simplify:
$$25x^{2} + 32p\,x + 16p^{2} - 144 = 0$$ $$-(1)$$

For tangency the quadratic in $$x$$ must have discriminant $$0$$:

$$\bigl(32p\bigr)^{2} - 4 \cdot 25 \bigl(16p^{2}-144\bigr) = 0$$

$$1024p^{2} - 1600p^{2} + 14400 = 0$$

$$-576p^{2} + 14400 = 0 \;\;\Longrightarrow\;\; 576p^{2} = 14400$$

$$p^{2} = 25 \;\;\Longrightarrow\;\; p = \pm 5$$

Thus the two tangent lines are
$$y = x + 5 \quad\text{and}\quad y = x - 5$$.

Case 2: Coordinates of the points of contact $$A$$ and $$B$$.

For a tangent quadratic $$ax^{2}+bx+c=0$$, at tangency $$x = -\dfrac{b}{2a}$$. In equation $$-(1)$$ we have $$a = 25,\; b = 32p$$, so

$$x = -\dfrac{32p}{2\cdot25} = -\dfrac{16p}{25}$$.

• For $$p = 5$$:
$$x_A = -\dfrac{16(5)}{25} = -\dfrac{16}{5},\qquad y_A = x_A + 5 = -\dfrac{16}{5} + \dfrac{25}{5} = \dfrac{9}{5}$$

• For $$p = -5$$:
$$x_B = -\dfrac{16(-5)}{25} = \dfrac{16}{5},\qquad y_B = x_B - 5 = \dfrac{16}{5} - \dfrac{25}{5} = -\dfrac{9}{5}$$

Hence
$$A\!\left(-\dfrac{16}{5},\;\dfrac{9}{5}\right),\quad B\!\left(\;\dfrac{16}{5},\;-\dfrac{9}{5}\right).$$

Case 3: Intersection points $$C$$ and $$D$$ of the line $$y = x$$ with the ellipse.

Put $$y = x$$ in the ellipse:

$$\dfrac{x^{2}}{16} + \dfrac{x^{2}}{9} = 1 \;\;\Longrightarrow\;\; x^{2}\Bigl(\dfrac{1}{16}+\dfrac{1}{9}\Bigr) = 1$$

$$x^{2}\Bigl(\dfrac{25}{144}\Bigr)=1 \;\;\Longrightarrow\;\; x^{2}=\dfrac{144}{25}$$

$$x = \pm\dfrac{12}{5}\;\;,\;\; y = x$$

Therefore
$$C\!\left(\dfrac{12}{5},\;\dfrac{12}{5}\right),\quad D\!\left(-\dfrac{12}{5},\;-\dfrac{12}{5}\right).$$

Case 4: Area of quadrilateral $$ABCD$$ (vertices taken in order $$C \rightarrow A \rightarrow D \rightarrow B$$, which goes anticlockwise).

Using the Shoelace Theorem:

Coordinates:
$$C\left(\dfrac{12}{5},\;\dfrac{12}{5}\right),\; A\left(-\dfrac{16}{5},\;\dfrac{9}{5}\right),\; D\left(-\dfrac{12}{5},-\dfrac{12}{5}\right),\; B\left(\;\dfrac{16}{5},-\dfrac{9}{5}\right)$$

Compute $$\sum x_i\,y_{i+1}$$:
$$\dfrac{12}{5}\!\cdot\!\dfrac{9}{5} + \left(-\dfrac{16}{5}\right)\!\cdot\!\left(-\dfrac{12}{5}\right) + \left(-\dfrac{12}{5}\right)\!\cdot\!\left(-\dfrac{9}{5}\right) + \dfrac{16}{5}\!\cdot\!\dfrac{12}{5} = \dfrac{108+192+108+192}{25} = \dfrac{600}{25} = 24$$

Compute $$\sum y_i\,x_{i+1}$$:
$$\dfrac{12}{5}\!\cdot\!\left(-\dfrac{16}{5}\right) + \dfrac{9}{5}\!\cdot\!\left(-\dfrac{12}{5}\right) + \left(-\dfrac{12}{5}\right)\!\cdot\!\dfrac{16}{5} + \left(-\dfrac{9}{5}\right)\!\cdot\!\dfrac{12}{5} = \dfrac{-192-108-192-108}{25} = -\dfrac{600}{25} = -24$$

Area
$$=\dfrac{1}{2}\Bigl|\;\sum x_i y_{i+1} - \sum y_i x_{i+1}\Bigr| =\dfrac{1}{2}\bigl|24 - (-24)\bigr| =\dfrac{1}{2}\times48 = 24.$$

Hence the area of quadrilateral $$ABCD$$ is $$24$$.

Therefore, Option B is correct.

The given ellipse is $$\frac{x^{2}}{18}+\frac{y^{2}}{9}=1$$.

Comparing with $$\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1$$ we get $$a^{2}=18,\;b^{2}=9$$.
Hence $$a=3\sqrt{2},\;b=3$$.

For an ellipse, $$c^{2}=a^{2}-b^{2}$$, so
$$c^{2}=18-9=9\;\Longrightarrow\;c=3$$.

The foci are $$S(-3,0)$$ and $$S'(3,0)$$.

Let an arbitrary point on the ellipse be $$P(x,y)$$. Because $$P$$ lies on the ellipse,

$$\frac{x^{2}}{18}+\frac{y^{2}}{9}=1 \quad\Longrightarrow\quad y^{2}=9\left(1-\frac{x^{2}}{18}\right)=9-\frac{x^{2}}{2}\;.$$ $$-(1)$$

Distances of $$P$$ from the two foci are

$$SP=\sqrt{(x+3)^{2}+y^{2}},\qquad S'P=\sqrt{(x-3)^{2}+y^{2}}.$$

We need the product $$SP\cdot S'P$$. First square each distance:

$$SP^{2}=(x+3)^{2}+y^{2},\qquad S'P^{2}=(x-3)^{2}+y^{2}.$$

Using $$(1)$$ to eliminate $$y^{2}$$:

$$SP^{2}=(x+3)^{2}+9-\frac{x^{2}}{2}$$ $$\phantom{SP^{2}}=\frac{x^{2}}{2}+6x+9+9 =\frac{x^{2}}{2}+6x+18,$$

$$S'P^{2}=(x-3)^{2}+9-\frac{x^{2}}{2}$$ $$\phantom{S'P^{2}}=\frac{x^{2}}{2}-6x+18.$$

Therefore

$$\bigl(SP\cdot S'P\bigr)^{2}=SP^{2}\,S'P^{2} =\left(\frac{x^{2}}{2}+6x+18\right)\left(\frac{x^{2}}{2}-6x+18\right).$$

Recognise the form $$(A+6x)(A-6x)=A^{2}-36x^{2},$$ where $$A=\dfrac{x^{2}}{2}+18$$. Hence

$$\bigl(SP\cdot S'P\bigr)^{2} =\left(\frac{x^{2}}{2}+18\right)^{2}-36x^{2}.$$ Expand: $$\bigl(SP\cdot S'P\bigr)^{2} =\frac{x^{4}}{4}+18x^{2}+324-36x^{2} =\frac{x^{4}}{4}-18x^{2}+324.$$ Let $$X=x^{2}\;(X\ge 0)$$ to work with one variable: $$\bigl(SP\cdot S'P\bigr)^{2} =\frac{X^{2}}{4}-18X+324.$$ $$-(2)$$

The point $$P$$ lies on the ellipse, so $$x^{2}\le a^{2}=18$$, that is $$0\le X\le 18$$.

Equation $$(2)$$ is a quadratic in $$X$$ with coefficient $$\frac14>0$$; it opens upward. Its vertex is at

$$X_v=\frac{-(-18)}{2\left(\frac14\right)} =\frac{18}{0.5}=36.$$

The vertex lies to the right of the allowed interval $$[0,18]$$, so within the interval the quadratic is strictly decreasing.
Hence:

• Maximum of $$(SP\cdot S'P)^{2}$$ occurs at the left end $$X=0$$.
• Minimum of $$(SP\cdot S'P)^{2}$$ occurs at the right end $$X=18$$.

From $$(2):\;\bigl(SP\cdot S'P\bigr)^{2}=324 \;\Longrightarrow\;SP\cdot S'P=18.$$

Substitute $$X=18$$ in $$(2):$$ $$\bigl(SP\cdot S'P\bigr)^{2} =\frac{(18)^{2}}{4}-18(18)+324 =81-324+324=81,$$ $$\Longrightarrow\;SP\cdot S'P=9.$$

Thus

$$\min(SP\cdot S'P)=9,\qquad \max(SP\cdot S'P)=18.$$

Required sum:

$$\min(SP\cdot S'P)+\max(SP\cdot S'P)=9+18=27.$$

Option D is correct.

To find the maximum area of the triangle $$PQR$$, we determine the equations of the ellipse, the enclosing circle, and the line containing the base $$QR$$.

Step 1: Find the Equation of the Ellipse $$E$$

The general equation of the ellipse is given by:

$$E : \frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$

We are given the eccentricity $$e = \frac{1}{2}$$ and the foci at $$(\pm 2, 0)$$. The coordinates of the foci are defined as $$(\pm ae, 0)$$:

$$ae = 2 \implies a\left(\frac{1}{2}\right) = 2 \implies a = 4$$

Using the relationship $$b^2 = a^2(1 - e^2)$$:

$$b^2 = 16\left(1 - \frac{1}{4}\right) = 16 \times \frac{3}{4} = 12 \implies b = 2\sqrt{3}$$

Thus, the point of intersection of the ellipse with the negative y-axis is $$(0, -b) = (0, -2\sqrt{3})$$.

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Step 2: Determine the Circle $$C$$ of Minimum Area Enclosing $$E$$

For an ellipse where $$a^2 \le 2b^2$$, the circle of minimum area enclosing it is centered at the origin with a radius equal to the semi-major axis $$a$$.

Checking our values:

$$a^2 = 16 \quad \text{and} \quad 2b^2 = 2 \times 12 = 24$$

Since $$16 \le 24$$, the radius of the circle $$C$$ is $$R = a = 4$$.

The equation of the enclosing circle $$C$$ is:

$$x^2 + y^2 = 16$$

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Step 3: Identify the Line containing the Side $$QR$$

The side $$QR$$ is parallel to the major axis (x-axis) and passes through the point of intersection with the negative y-axis $$(0, -2\sqrt{3})$$. Therefore, the equation of the line containing $$QR$$ is:

$$y = -2\sqrt{3}$$

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Step 4: Calculate the Maximum Area of Triangle $$PQR$$

The area of a triangle is given by the formula:

$$\text{Area} = \frac{1}{2} \times \text{base} \times \text{height}$$

The base length is given as $$2a = 8$$.

The vertex $$P$$ lies on the circle $$x^2 + y^2 = 16$$, where the y-coordinates range from $$-4$$ to $$4$$. To maximize the height $$h$$ (the vertical distance from $$P$$ to the line $$y = -2\sqrt{3}$$), we pick the top-most point on the circle $$P(0, 4)$$:

$$h_{\text{max}} = 4 - (-2\sqrt{3}) = 4 + 2\sqrt{3}$$

Evaluating the maximum area expression:

$$\text{Maximum Area} = \frac{1}{2} \times 8 \times (4 + 2\sqrt{3}) = 4(4 + 2\sqrt{3}) = 16 + 8\sqrt{3} = 8(2 + \sqrt{3})$$

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Therefore, the maximum area of the triangle $$PQR$$ is equal to $$8(2 + \sqrt{3})$$.

Let the centre of the ellipse $$\dfrac{x^{2}}{a^{2}}+\dfrac{y^{2}}{b^{2}}=1$$ be the origin $$O(0,0)$$.
Because the length of the major axis is given as 17,

$$2a = 17 \; \Longrightarrow \; a = \dfrac{17}{2}$$

For an ellipse, the distance of each focus from the centre is $$c$$ where

$$c^{2}=a^{2}-b^{2} \quad -(1)$$

The foci are therefore $$F_{1}(-c,0)$$ and $$F_{2}(c,0)$$.

The circle $$C$$ is also centred at $$O$$ and passes through the foci, hence its radius is $$c$$ and its equation is

$$x^{2}+y^{2}=c^{2} \quad -(2)$$

Let $$P(x,y)$$ be one of the four common points of the ellipse and the circle.
Then $$P$$ satisfies both $$(2)$$ and the ellipse equation, giving

$$\dfrac{x^{2}}{a^{2}}+\dfrac{y^{2}}{b^{2}}=1 \quad -(3)$$

From $$(2)$$: $$y^{2}=c^{2}-x^{2} \quad -(4)$$

Substitute $$(4)$$ into $$(3)$$:

$$\dfrac{x^{2}}{a^{2}}+\dfrac{c^{2}-x^{2}}{b^{2}}=1$$

Simplify the left side:

$$x^{2}\left(\dfrac{1}{a^{2}}-\dfrac{1}{b^{2}}\right)+\dfrac{c^{2}}{b^{2}}=1$$

Using $$(1)$$, $$b^{2}=a^{2}-c^{2}$$, so

$$\dfrac{1}{a^{2}}-\dfrac{1}{b^{2}}=\dfrac{b^{2}-a^{2}}{a^{2}b^{2}}=-\dfrac{c^{2}}{a^{2}b^{2}}$$

Hence

$$-\dfrac{c^{2}}{a^{2}b^{2}}\,x^{2}+\dfrac{c^{2}}{b^{2}}=1$$

Multiply by $$b^{2}$$:

$$c^{2}-\dfrac{c^{2}}{a^{2}}\,x^{2}=b^{2}$$

Replace $$b^{2}$$ again by $$a^{2}-c^{2}$$:

$$c^{2}-\dfrac{c^{2}}{a^{2}}\,x^{2}=a^{2}-c^{2}$$

Rearrange to solve for $$x^{2}$$:

$$\dfrac{c^{2}}{a^{2}}\,x^{2}=2c^{2}-a^{2}$$

$$x^{2}=a^{2}\dfrac{2c^{2}-a^{2}}{c^{2}} \quad -(5)$$

Now obtain $$y^{2}$$ from $$(4)$$:

$$y^{2}=c^{2}-x^{2}=c^{2}-a^{2}\dfrac{2c^{2}-a^{2}}{c^{2}} \quad -(6)$$

Next use the area condition.
For the triangle with vertices $$P, F_{1}(-c,0), F_{2}(c,0)$$:

• Base $$F_{1}F_{2}=2c$$.
• The altitude from $$P$$ to the base is $$|y|$$ (since the base lies on the $$x$$-axis).

Hence

$$\text{Area}=\dfrac{1}{2}\times 2c \times |y|=c|y|$$

The area is given as 30, so

$$c|y| = 30 \;\Longrightarrow\; y^{2}=\dfrac{900}{c^{2}} \quad -(7)$$

Equate $$(6)$$ and $$(7)$$:

$$\dfrac{900}{c^{2}} = c^{2}-a^{2}\dfrac{2c^{2}-a^{2}}{c^{2}}$$

Multiply by $$c^{2}$$ to clear denominators:

$$900 = c^{4}-a^{2}(2c^{2}-a^{2}) \quad -(8)$$

Insert $$a^{2}=\left(\dfrac{17}{2}\right)^{2}=\dfrac{289}{4}$$ into $$(8)$$:

$$900 = c^{4}-\dfrac{289}{4}\left(2c^{2}-\dfrac{289}{4}\right)$$

Multiply by 16 to avoid fractions:

$$16c^{4}-8\!\cdot\!289\,c^{2}+289^{2}-14400=0$$

That is

$$16c^{4}-2312c^{2}+69121=0$$

Let $$k=c^{2}$$. The quadratic in $$k$$ becomes

$$16k^{2}-2312k+69121=0$$

Using the quadratic formula,

$$k=\dfrac{2312\pm\sqrt{2312^{2}-4\!\cdot\!16\!\cdot\!69121}}{32}$$

The discriminant is

$$2312^{2}-64\!\cdot\!69121 = 5345344-4423744 = 921600 = 960^{2}$$

Hence

$$k=\dfrac{2312\pm960}{32}$$

This gives two values: $$k=102.25$$ and $$k=42.25$$.
But $$k=c^{2}$$ must satisfy $$c^{2}\lt a^{2}=72.25$$, so we take

$$c^{2}=42.25 \;=\;\left(6.5\right)^{2}$$

Therefore

$$c = 6.5, \quad 2c = 13$$

The distance between the foci of the ellipse is 13.
Hence the correct option is Option B (13).

The two foci are $$(2,5)$$ and $$(2,-3)$$. Their common $$x$$-coordinate is $$2$$, so the major axis is the vertical line $$x = 2$$.

For an ellipse with vertical major axis and centre $$(h,k)$$, the standard form is
$$\frac{(x-h)^2}{b^2} + \frac{(y-k)^2}{a^2} = 1$$ with $$a \gt b$$, foci $$(h,\,k \pm c)$$, and relations $$c^2 = a^2 - b^2$$, $$e = \frac{c}{a}$$.

Step 1: Find $$c$$
Distance between the given foci:
$$2c = |5 - (-3)| = 8$$
$$\Rightarrow c = 4$$.

Step 2: Find $$a$$ using eccentricity
Given $$e = \frac{4}{5}$$ and $$e = \frac{c}{a}$$,
$$\frac{4}{5} = \frac{4}{a} \;\Rightarrow\; a = 5$$.

Step 3: Find $$b$$
Using $$c^2 = a^2 - b^2$$:
$$4^2 = 5^2 - b^2$$
$$16 = 25 - b^2$$
$$b^2 = 25 - 16 = 9$$
$$\Rightarrow b = 3$$.

Step 4: Length of the latus-rectum
For any ellipse, length of latus-rectum $$L = \frac{2b^2}{a}$$.
Substituting $$b^2 = 9$$ and $$a = 5$$:
$$L = \frac{2 \times 9}{5} = \frac{18}{5}$$.

Hence, the length of the latus-rectum is $$\frac{18}{5}$$.

Option D is correct.

We are given the ellipse $$\frac{x^2}{9} + \frac{y^2}{4} = 1$$ with midpoint of a chord at $$(\sqrt{2}, \frac{4}{3})$$.

We start by finding the equation of the chord with midpoint $$(h, k)$$ in the standard form of an ellipse $$\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$, which is given by $$\frac{xh}{a^2} + \frac{yk}{b^2} = \frac{h^2}{a^2} + \frac{k^2}{b^2}$$.

Substituting $$a^2 = 9$$, $$b^2 = 4$$, $$h = \sqrt{2}$$, and $$k = \frac{4}{3}$$ into this formula yields $$\frac{\sqrt{2}x}{9} + \frac{4y}{3 \cdot 4} = \frac{2}{9} + \frac{16}{36}$$, which simplifies to $$\frac{\sqrt{2}x}{9} + \frac{y}{3} = \frac{2}{3}$$. Multiplying through by 9 gives $$\sqrt{2}x + 3y = 6$$, so $$y = \frac{6 - \sqrt{2}x}{3}$$.

Next, we find the endpoints of the chord by substituting this expression for $$y$$ into the ellipse equation: $$\frac{x^2}{9} + \frac{1}{4}\left(\frac{6 - \sqrt{2}x}{3}\right)^2 = 1$$, which is equivalent to $$\frac{x^2}{9} + \frac{(6 - \sqrt{2}x)^2}{36} = 1$$. Multiplying both sides by 36 leads to $$4x^2 + (6 - \sqrt{2}x)^2 = 36$$, and expanding gives $$4x^2 + 36 - 12\sqrt{2}x + 2x^2 = 36$$. This simplifies to $$6x^2 - 12\sqrt{2}x = 0$$ or $$6x(x - 2\sqrt{2}) = 0$$, so the solutions are $$x_1 = 0$$ and $$x_2 = 2\sqrt{2}$$.

When $$x = 0$$, we have $$y = \frac{6}{3} = 2$$, giving the point $$(0, 2)$$, and when $$x = 2\sqrt{2}$$, we get $$y = \frac{6 - \sqrt{2} \cdot 2\sqrt{2}}{3} = \frac{6 - 4}{3} = \frac{2}{3}$$, giving the point $$(2\sqrt{2}, \frac{2}{3})$$.

To verify the midpoint, we compute $$\left(\frac{0 + 2\sqrt{2}}{2}, \frac{2 + \frac{2}{3}}{2}\right) = \left(\sqrt{2}, \frac{4}{3}\right)$$, which matches the given midpoint.

Then the length of the chord is $$\sqrt{(2\sqrt{2} - 0)^2 + \left(\frac{2}{3} - 2\right)^2} = \sqrt{8 + \frac{16}{9}} = \sqrt{\frac{72 + 16}{9}} = \frac{\sqrt{88}}{3} = \frac{2\sqrt{22}}{3}$$.

Comparing this result with the given expression $$\frac{2\sqrt{\alpha}}{3}$$ shows that $$\alpha = 22$$, so the correct answer is 22.

For the first ellipse $$\dfrac{x^{2}}{b^{2}}+\dfrac{y^{2}}{25}=1$$ the larger denominator is $$25$$, so the semi-major axis length is $$a_1 = 5$$ and the semi-minor axis length is $$b_1 = b$$.

Eccentricity of an ellipse is given by $$e=\sqrt{1-\dfrac{b^{2}}{a^{2}}}$$.
Hence $$e_1 = \sqrt{1-\dfrac{b^{2}}{25}} \quad -(1)$$

For the hyperbola $$\dfrac{x^{2}}{16}-\dfrac{y^{2}}{b^{2}}=1$$ the semi-transverse axis is $$a_2 = 4$$ and the semi-conjugate axis is $$b_2 = b$$.

Eccentricity of a hyperbola is given by $$e=\sqrt{1+\dfrac{b^{2}}{a^{2}}}$$.
Hence $$e_2 = \sqrt{1+\dfrac{b^{2}}{16}} \quad -(2)$$

Given $$e_1\,e_2 = 1$$. Substituting from $$(1)$$ and $$(2)$$:

$$\sqrt{1-\dfrac{b^{2}}{25}}\;\sqrt{1+\dfrac{b^{2}}{16}} = 1$$

Squaring both sides:

$$\left(1-\dfrac{b^{2}}{25}\right)\!\left(1+\dfrac{b^{2}}{16}\right)=1$$

Expanding and simplifying:

$$1+\dfrac{b^{2}}{16}-\dfrac{b^{2}}{25}-\dfrac{b^{4}}{400}=1$$
$$\dfrac{b^{2}}{16}-\dfrac{b^{2}}{25}-\dfrac{b^{4}}{400}=0$$
$$b^{2}\left(\dfrac{1}{16}-\dfrac{1}{25}\right)-\dfrac{b^{4}}{400}=0$$
$$b^{2}\left(\dfrac{9}{400}\right)-\dfrac{b^{4}}{400}=0$$
$$\dfrac{b^{2}}{400}\Bigl(9-b^{2}\Bigr)=0$$

Since $$b\neq 0$$, we get $$b^{2}=9 \Rightarrow b=3 \;(\text{given } b\lt 5).$$

Now compute the four focal points:

Eccentricity $$e_1 = \sqrt{1-\dfrac{9}{25}}=\dfrac{4}{5}$$.
Distance of each focus from the centre: $$c_1=a_1e_1=5\left(\dfrac{4}{5}\right)=4$$.
Ellipse foci: $$(0,\pm4).$$

Eccentricity $$e_2 = \sqrt{1+\dfrac{9}{16}}=\dfrac{5}{4}$$.
Distance of each focus from the centre: $$c_2=a_2e_2=4\left(\dfrac{5}{4}\right)=5$$.
Hyperbola foci: $$(\pm5,0).$$

The required ellipse has its axes along the coordinate axes and must pass through all four foci $$(\pm5,0),\,(0,\pm4)$$. Take its equation as

$$\dfrac{x^{2}}{A^{2}}+\dfrac{y^{2}}{B^{2}}=1.$$

Substituting point $$(5,0):\; \dfrac{25}{A^{2}} = 1 \Rightarrow A^{2}=25 \Rightarrow A=5.$$

Substituting point $$(0,4):\; \dfrac{16}{B^{2}} = 1 \Rightarrow B^{2}=16 \Rightarrow B=4.$$

Thus the ellipse is $$\dfrac{x^{2}}{25}+\dfrac{y^{2}}{16}=1$$ with semi-major axis $$a=5$$ and semi-minor axis $$b=4$$ (since $$25\gt16$$).

Eccentricity of this ellipse is

$$e = \sqrt{1-\dfrac{b^{2}}{a^{2}}} = \sqrt{1-\dfrac{16}{25}} = \sqrt{\dfrac{9}{25}} = \dfrac{3}{5}.$$

Therefore, the required eccentricity is $$\dfrac{3}{5}$$.

Option B is correct.

The ellipse is given by $$E: \frac{x^2}{a^2}+\frac{y^2}{b^2}=1, a > b$$ and the hyperbola by $$H: \frac{x^2}{A^2}-\frac{y^2}{B^2}=1$$. The distance between the foci of $$E$$ is $$2ae$$, while that of $$H$$ is $$2Ae_H$$, and it is given that $$2ae = 2Ae_H = 2\sqrt{3}$$, so that $$ae = Ae_H = \sqrt{3}$$. Additionally, $$a - A = 2$$ and $$\frac{e}{e_H} = \frac{1}{3}$$, i.e., $$e_H = 3e$$.

From $$ae = \sqrt{3}$$ it follows that $$e = \frac{\sqrt{3}}{a}$$. Since $$e_H = 3e = \frac{3\sqrt{3}}{a}$$ and $$Ae_H = \sqrt{3}$$, we have $$A \cdot \frac{3\sqrt{3}}{a} = \sqrt{3} \Rightarrow A = \frac{a}{3}$$. Substituting into $$a - A = 2$$ yields $$a - \frac{a}{3} = 2 \Rightarrow \frac{2a}{3} = 2 \Rightarrow a = 3$$, hence $$A = 1$$, $$e = \frac{\sqrt{3}}{3} = \frac{1}{\sqrt{3}}$$, and $$e_H = \sqrt{3}$$.

For the ellipse, $$b^2 = a^2(1-e^2) = 9(1-\frac{1}{3}) = 6$$, and for the hyperbola, $$B^2 = A^2(e_H^2-1) = 1(3-1) = 2$$.

The length of the latus rectum of the ellipse is $$\frac{2b^2}{a} = \frac{12}{3} = 4$$, and that of the hyperbola is $$\frac{2B^2}{A} = \frac{4}{1} = 4$$, so that the sum is $$4 + 4 = 8$$.

The sum of lengths of latus rectums is 8, which matches Option C. Therefore, the answer is Option C.

The given circle is $$x^{2}+(y-1)^{2}=2$$.
Its centre is $$O(0,1)$$ and its radius is $$\sqrt{2}$$.

The straight line is $$x+y=3 \;\; \Longleftrightarrow \;\; x+y-3=0$$.
Distance of the centre $$O(0,1)$$ from this line is $$\frac{|0+1-3|}{\sqrt{1^{2}+1^{2}}}= \frac{2}{\sqrt{2}}=\sqrt{2}$$, that is exactly the radius, hence the line is tangent to the circle.

For a circle, the point of contact is the foot of the perpendicular drawn from the centre to the tangent. For the line $$x+y-3=0$$ the foot of the perpendicular from $$(x_{0},y_{0})$$ is $$\left(x_{0}-a\frac{ax_{0}+by_{0}+c}{a^{2}+b^{2}},\;y_{0}-b\frac{ax_{0}+by_{0}+c}{a^{2}+b^{2}}\right)$$ with $$a=1,\;b=1,\;c=-3,\;(x_{0},y_{0})=(0,1).$$ Thus

$$x_{1}=0-\frac{1(-2)}{2}=1, \qquad y_{1}=1-\frac{1(-2)}{2}=2.$$

Therefore $$P(1,2)$$ and $$x_{1}y_{1}=2.$$

Since the same straight line touches the two ellipses $$E_{1},E_{2}$$ at $$Q(x_{2},y_{2})$$ and $$R(x_{3},y_{3})$$, both points lie on the line: $$x_{2}+y_{2}=3, \qquad x_{3}+y_{3}=3 \; -(1)$$

The midpoint condition $$P$$ is the midpoint of $$QR$$:

$$\frac{x_{2}+x_{3}}{2}=1, \qquad \frac{y_{2}+y_{3}}{2}=2 \; -(2)$$

Let $$x_{2}=u \;\; (\Rightarrow y_{2}=3-u)$$. From $$(2)$$, $$x_{3}=2-u$$ and with $$(1)$$, $$y_{3}=3-(2-u)=1+u.$$ Hence

$$Q(u,\,3-u), \qquad R(2-u,\,1+u).$$

The distance $$PQ$$ is given to be $$\dfrac{2\sqrt{2}}{3}$$. Compute $$PQ^{2}:$$

$$PQ^{2}=(u-1)^{2}+\bigl((3-u)-2\bigr)^{2} =(u-1)^{2}+(1-u)^{2}=2(u-1)^{2}.$$

Therefore $$\sqrt{2}\,|u-1|=\frac{2\sqrt{2}}{3}\;\Longrightarrow\;|u-1|=\frac{2}{3}.$$ So

$$u=1+\frac{2}{3}=\frac{5}{3}\quad\text{or}\quad u=1-\frac{2}{3}=\frac{1}{3}.$$

This merely swaps $$Q$$ and $$R$$; either choice gives the same final value. Choose $$u=\dfrac{5}{3}$$ (the other works identically):

$$Q\!\left(\frac{5}{3},\,\frac{4}{3}\right), \qquad R\!\left(\frac{1}{3},\,\frac{8}{3}\right).$$

Now compute the required sum:

$$x_{1}y_{1}=1\cdot2=2,$$ $$x_{2}y_{2}=\frac{5}{3}\cdot\frac{4}{3}=\frac{20}{9},$$ $$x_{3}y_{3}=\frac{1}{3}\cdot\frac{8}{3}=\frac{8}{9}.$$

Hence $$x_{1}y_{1}+x_{2}y_{2}+x_{3}y_{3}=2+\frac{20}{9}+\frac{8}{9}=2+\frac{28}{9}=\frac{46}{9}.$$

Finally, $$9\bigl(x_{1}y_{1}+x_{2}y_{2}+x_{3}y_{3}\bigr)=9\cdot\frac{46}{9}=46.$$

The desired value is $$46$$.

We have ellipse $$E_1: \frac{x^2}{9} + \frac{y^2}{4} = 1$$ with semi-major axis $$a_1 = 3$$, semi-minor axis $$b_1 = 2$$.

Eccentricity: $$e = \sqrt{1 - \frac{b_1^2}{a_1^2}} = \sqrt{1 - \frac{4}{9}} = \frac{\sqrt{5}}{3}$$.

For each ellipse $$E_i$$, the length of the minor axis of $$E_i$$ equals the length of the major axis of $$E_{i+1}$$.

All ellipses share the same center and eccentricity $$e = \frac{\sqrt{5}}{3}$$.

For any ellipse with eccentricity $$e$$: $$b^2 = a^2(1-e^2) = a^2 \cdot \frac{4}{9}$$, so $$b = \frac{2a}{3}$$.

Since the minor axis of $$E_i$$ (length $$2b_i$$) = major axis of $$E_{i+1}$$ (length $$2a_{i+1}$$):

$$a_{i+1} = b_i = \frac{2}{3}a_i$$

So $$a_i = 3 \cdot \left(\frac{2}{3}\right)^{i-1}$$ and $$b_i = \frac{2}{3}a_i = 2 \cdot \left(\frac{2}{3}\right)^{i-1}$$.

$$ A_i = \pi a_i b_i = \pi \cdot 3\left(\frac{2}{3}\right)^{i-1} \cdot 2\left(\frac{2}{3}\right)^{i-1} = 6\pi\left(\frac{2}{3}\right)^{2(i-1)} = 6\pi\left(\frac{4}{9}\right)^{i-1} $$

$$ \sum_{i=1}^{\infty} A_i = 6\pi \sum_{i=1}^{\infty}\left(\frac{4}{9}\right)^{i-1} = 6\pi \cdot \frac{1}{1 - 4/9} = 6\pi \cdot \frac{9}{5} = \frac{54\pi}{5} $$

$$ \frac{5}{\pi}\left(\sum_{i=1}^{\infty} A_i\right) = \frac{5}{\pi} \cdot \frac{54\pi}{5} = 54 $$

Hence the answer is 54.

Focal distances of $$(x,y)$$ are $$a \pm ex$$. Product $$= a^2 - e^2x^2 = 7/4$$.

Point $$(\sqrt{3}, 1/2)$$ is on ellipse: $$\frac{3}{a^2} + \frac{1}{4b^2} = 1$$. Use $$b^2 = a^2(1-e^2)$$.

Solving the system of equations gives two values for $$e$$. 

Their Difference $$\frac{3-2\sqrt{2}}{2\sqrt{3}}$$.

For an ellipse centred at the origin with the major axis along the $$x$$-axis, we use the standard form

$$\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1,\qquad a \gt b\,(\,\text{major}\, \gt \text{minor}\,)$$

Eccentricity: $$e=\sqrt{1-\frac{b^{2}}{a^{2}}}$$
Distance between the two foci: $$2ae$$
Length of the minor axis: $$2b$$

The question states: “length of the minor axis is one fourth of the distance between the foci”.
Translate this directly into an equation:

$$2b=\frac{1}{4}\times(2ae)$$

Simplify:

$$2b=\frac{ae}{2}\qquad\Longrightarrow\qquad4b=ae$$ $$-(1)$$

Replace $$b$$ by its expression in terms of $$a$$ and $$e$$. From the definition of eccentricity,

$$b=a\sqrt{1-e^{2}}$$ $$-(2)$$

Substitute $$(2)$$ into $$(1)$$:

$$4\bigl(a\sqrt{1-e^{2}}\bigr)=ae$$

Assuming $$a\neq0$$, divide both sides by $$a$$:

$$4\sqrt{1-e^{2}}=e$$

Square both sides to eliminate the square root:

$$16(1-e^{2})=e^{2}$$

Expand and collect like terms:

$$16-16e^{2}=e^{2}\qquad\Longrightarrow\qquad17e^{2}=16$$

Solve for $$e$$:

$$e^{2}=\frac{16}{17}\qquad\Longrightarrow\qquad e=\frac{4}{\sqrt{17}}$$

Since $$e$$ must be positive and less than 1, this value is acceptable.
Hence, the eccentricity of the ellipse is $$\frac{4}{\sqrt{17}}$$.

Option A is correct.

The ellipse is $$\frac{x^{2}}{25} + \frac{y^{2}}{16} = 1$$. Write it in the standard form $$S = 0$$, where

$$S = \frac{x^{2}}{25} + \frac{y^{2}}{16} - 1 = 0$$.
If $$(x_1 , y_1)$$ is the mid-point of a chord of the conic $$S = 0$$, then the chord is given by $$T = S_1$$, where

$$T$$ is obtained from $$S$$ by replacing $$x^{2}$$ with $$x x_1$$ and $$y^{2}$$ with $$y y_1$$, and $$S_1$$ is obtained by replacing $$x, y$$ in $$S$$ with $$x_1 , y_1$$.

For our ellipse and mid-point $$(3,1)$$:

$$T = \frac{x\,x_1}{25} + \frac{y\,y_1}{16} - 1 = \frac{3x}{25} + \frac{1\;y}{16} - 1$$.

$$S_1 = \frac{x_1^{2}}{25} + \frac{y_1^{2}}{16} - 1 = \frac{3^{2}}{25} + \frac{1^{2}}{16} - 1 = \frac{9}{25} + \frac{1}{16} - 1$$.

Take the common denominator $$400$$: $$\frac{9}{25} = \frac{144}{400}, \quad \frac{1}{16} = \frac{25}{400}.$$ Hence

$$S_1 = \frac{144 + 25}{400} - 1 = \frac{169}{400} - 1 = -\frac{231}{400}.$$

Equating $$T$$ and $$S_1$$:

$$\frac{3x}{25} + \frac{y}{16} - 1 = -\frac{231}{400}.$$

Multiply every term by $$400$$ to remove fractions:

$$400 \left(\frac{3x}{25}\right) + 400 \left(\frac{y}{16}\right) - 400 = -231.$$ $$48x + 25y - 400 = -231.$$

$$48x + 25y - 400 + 231 = 0$$ $$48x + 25y - 169 = 0.$$

Therefore, the chord with mid-point $$(3,1)$$ is

$$48x + 25y = 169.$$ Hence, Option A is correct.

The ellipse is $$\frac{x^{2}}{36} + \frac{y^{2}}{25} = 1$$ and the external point is $$P(\sqrt{5},\sqrt{5})$$.
Let a variable line through P have slope $$m$$. Its equation can be written in parametric form as

$$x = \sqrt{5} + t ,\; y = \sqrt{5} + mt \qquad (t\in\mathbb{R})$$
The point $$P$$ corresponds to $$t = 0$$. The intersections with the ellipse (points $$A,\,B$$) occur for those values of $$t$$ that satisfy

$$\frac{(\sqrt{5}+t)^{2}}{36} + \frac{(\sqrt{5}+mt)^{2}}{25} = 1$$

Expand each square:
$$(\sqrt{5}+t)^{2}=5+2\sqrt{5}\,t+t^{2},\qquad (\sqrt{5}+mt)^{2}=5+2m\sqrt{5}\,t+m^{2}t^{2}$$

Substituting and clearing denominators by multiplying by $$900 \;(=36\!\cdot\!25)$$ gives

$$(25+36m^{2})t^{2}+\sqrt{5}(50+72m)\,t-595=0\tag{1}$$

Equation $$(1)$$ is quadratic in $$t$$, so its roots $$t_{1},t_{2}$$ represent the directed distances (along the x-axis direction of the line) from $$P$$ to $$A,\,B$$ respectively.

For a quadratic $$At^{2}+Bt+C=0$$ we have $$t_{1}t_{2}=C/A.$$
Here
$$A = 25+36m^{2},\quad C = -595 \;\Rightarrow\; t_{1}t_{2}= \frac{-595}{25+36m^{2}}$$

The actual (positive) distances are $$PA = |t_{1}|\sqrt{1+m^{2}},\; PB = |t_{2}|\sqrt{1+m^{2}}.$$
Hence

$$PA\cdot PB = |t_{1}t_{2}|(1+m^{2}) = \frac{595(1+m^{2})}{25+36m^{2}}\tag{2}$$

To maximise $$PA\cdot PB$$ we maximise the function
$$g(m)=\frac{1+m^{2}}{25+36m^{2}},\qquad m\in\mathbb{R}$$

Set $$t=m^{2}\ge 0.$$ Then $$g(t)=\frac{1+t}{25+36t}.$$ Differentiate:

$$\frac{dg}{dt}= \frac{(25+36t)\cdot1 - (1+t)\cdot36}{(25+36t)^{2}} = \frac{25+36t-36-36t}{(25+36t)^{2}} = \frac{-11}{(25+36t)^{2}} \lt 0$$

Since $$dg/dt$$ is negative for all $$t\ge 0$$, $$g(t)$$ decreases as $$t$$ increases. Therefore $$g(t)$$ (and hence $$PA\cdot PB$$) is maximum at $$t = 0$$, i.e. at $$m = 0$$.

Thus the required line is horizontal: $$y = \sqrt{5}.$$
Its intersections with the ellipse are obtained by substituting $$y=\sqrt{5}:$$

$$\frac{x^{2}}{36} + \frac{5}{25}=1 \;\Longrightarrow\; \frac{x^{2}}{36}=1-\frac{1}{5}=\frac{4}{5} \;\Longrightarrow\; x^{2}=\frac{144}{5}$$

Hence the points are $$A\bigl(\;+\frac{12}{\sqrt{5}},\,\sqrt{5}\bigr)$$ and $$B\bigl(\;-\frac{12}{\sqrt{5}},\,\sqrt{5}\bigr).$$

Compute the distances from $$P(\sqrt{5},\sqrt{5})$$:
$$PA = \left|\frac{12}{\sqrt{5}}-\sqrt{5}\right| = \left|\frac{12-5}{\sqrt{5}}\right| = \frac{7}{\sqrt{5}},$$
$$PB = \left|-\frac{12}{\sqrt{5}}-\sqrt{5}\right| = \left|\frac{-12-5}{\sqrt{5}}\right| = \frac{17}{\sqrt{5}}.$$

Now evaluate $$5(PA^{2}+PB^{2}):$$
$$PA^{2} = \frac{49}{5},\qquad PB^{2} = \frac{289}{5}$$
$$PA^{2}+PB^{2} = \frac{49+289}{5} = \frac{338}{5}$$
$$\therefore\; 5(PA^{2}+PB^{2}) = 5\cdot\frac{338}{5} = 338$$

Hence $$5(PA^{2}+PB^{2}) = 338,$$ which matches Option D.

The ellipse is $$\frac{x^{2}}{9}+\frac{y^{2}}{4}=1$$ and the circle $$\mathcal{C}$$ is $$x^{2}+y^{2}=9$$ (radius $$3$$, centre at the origin $$O(0,0)$$).
The point $$M$$ is $$(3,0)$$, so the ray $$OM$$ is the positive $$x$$-axis.

Because $$\angle ROM=\frac{\pi}{6}$$ and $$|OR|=3$$, the point $$R$$ on the circle is obtained by standard polar-Cartesian conversion:

$$R=\bigl(3\cos\frac{\pi}{6},\,3\sin\frac{\pi}{6}\bigr)=\left(\frac{3\sqrt{3}}{2},\,\frac{3}{2}\right).$$

Similarly, $$\angle SOM=\frac{\pi}{3}$$ gives

$$S=\bigl(3\cos\frac{\pi}{3},\,3\sin\frac{\pi}{3}\bigr)=\left(\frac{3}{2},\,\frac{3\sqrt{3}}{2}\right).$$

The vertical lines through $$R$$ and $$S$$ intersect the ellipse at $$P$$ and $$Q$$, so

$$x_{1}=x_{R}=\frac{3\sqrt{3}}{2},\qquad x_{2}=x_{S}=\frac{3}{2}.$$

Point P
Insert $$x_{1}$$ in the ellipse:

$$\frac{x_{1}^{2}}{9}=\frac{\left(\dfrac{3\sqrt{3}}{2}\right)^{2}}{9}=\frac{27/4}{9}=\frac34.$$

Therefore $$\frac{y_{1}^{2}}{4}=1-\frac34=\frac14 \;\Longrightarrow\; y_{1}=1 \;(\text{positive branch}).$$

Hence $$P=\left(\frac{3\sqrt{3}}{2},\,1\right).$$

Point Q
Insert $$x_{2}$$ in the ellipse:

$$\frac{x_{2}^{2}}{9}=\frac{\left(\dfrac{3}{2}\right)^{2}}{9}=\frac{9/4}{9}=\frac14.$$

Therefore $$\frac{y_{2}^{2}}{4}=1-\frac14=\frac34 \;\Longrightarrow\; y_{2}=\sqrt{3}.$$

Hence $$Q=\left(\frac{3}{2},\,\sqrt{3}\right).$$

Equation of line $$PQ$$
Slope $$m=\dfrac{\sqrt{3}-1}{\frac{3}{2}-\frac{3\sqrt{3}}{2}} =\dfrac{\sqrt{3}-1}{\frac{3}{2}(1-\sqrt{3})} =-\frac{2}{3}.$$

Using point $$P$$:

$$y-1=-\frac{2}{3}\Bigl(x-\frac{3\sqrt{3}}{2}\Bigr) \;\Longrightarrow\;3y-3=-2x+3\sqrt{3}.$$

Rearranging,

$$2x+3y=3(1+\sqrt{3}).$$

This matches Option A. Option B (with $$2x+y$$) is therefore incorrect.

Checking Statement C
Take $$N_{2}=(x_{2},0)=\left(\dfrac32,0\right).$$
Because $$Q$$ and $$S$$ have the same $$x$$-coordinate $$x_{2},$$ the required distances are vertical:

$$|N_{2}Q|=|y_{2}|=\sqrt{3},\qquad |N_{2}S|=\left|\frac{3\sqrt{3}}{2}\right|=\frac{3\sqrt{3}}{2}.$$

Thus $$3|N_{2}Q|=3\sqrt{3},\qquad 2|N_{2}S|=2\cdot\frac{3\sqrt{3}}{2}=3\sqrt{3},$$ so $$3|N_{2}Q|=2|N_{2}S|.$$
Statement C is true.

Checking Statement D
Take $$N_{1}=(x_{1},0)=\left(\dfrac{3\sqrt{3}}{2},0\right).$$

Vertical distances give $$|N_{1}P|=1,\quad |N_{1}R|=\frac{3}{2}.$$

But $$9|N_{1}P|=9,\quad 4|N_{1}R|=4\cdot\frac32=6,$$ which are not equal. Hence Statement D is false.

Final result
Option A and Option C are the only correct statements.

Correct choices: Option A, Option C.

Consider the ellipse $$\frac{x^2}{4}+\frac{y^2}{2}=1$$ and let the midpoint of a chord be $$(1, 1/2)$$. For an ellipse $$\frac{x^2}{a^2}+\frac{y^2}{b^2}=1$$, a chord with midpoint $$(h,k)$$ is given by the equation $$\frac{xh}{a^2}+\frac{yk}{b^2} = \frac{h^2}{a^2}+\frac{k^2}{b^2}$$. Substituting $$a^2=4, b^2=2, h=1, k=1/2$$ yields

$$\frac{x}{4}+\frac{y/2}{2} = \frac{1}{4}+\frac{1/4}{2} = \frac{1}{4}+\frac{1}{8} = \frac{3}{8}$$

which simplifies to

$$\frac{x}{4}+\frac{y}{4} = \frac{3}{8} \implies x + y = \frac{3}{2} \implies y = \frac{3}{2}-x$$.

Substituting into the ellipse equation gives

$$\frac{x^2}{4}+\frac{(3/2-x)^2}{2}=1$$

which expands to

$$\frac{x^2}{4}+\frac{9/4-3x+x^2}{2}=1$$

and simplifies as

$$\frac{x^2}{4}+\frac{9}{8}-\frac{3x}{2}+\frac{x^2}{2}=1$$

leading to

$$\frac{3x^2}{4}-\frac{3x}{2}+\frac{1}{8}=0 \implies 6x^2-12x+1=0$$.

Solving this quadratic yields

$$x = \frac{12\pm\sqrt{144-24}}{12} = \frac{12\pm\sqrt{120}}{12} = \frac{12\pm2\sqrt{30}}{12} = 1\pm\frac{\sqrt{30}}{6}$$.

The difference between the two $$x$$-values is $$\Delta x = \frac{2\sqrt{30}}{6} = \frac{\sqrt{30}}{3}$$. Since $$y = 3/2-x$$, it follows that $$\Delta y = -\Delta x$$. Therefore the length of the chord is

$$\sqrt{(\Delta x)^2+(\Delta y)^2} = |\Delta x|\sqrt{2} = \frac{\sqrt{30}}{3}\cdot\sqrt{2} = \frac{\sqrt{60}}{3} = \frac{2\sqrt{15}}{3}$$.

The correct answer is Option 3: $$\frac{2}{3}\sqrt{15}$$.

The ellipse is $$\frac{x^{2}}{9}+\frac{y^{2}}{4}=1$$.
Hence $$a=3,\;b=2$$ and its centre is $$O(0,0)$$. The vertex with positive $$x$$-coordinate is $$R(3,0)$$.

Let the second point of contact in the fourth quadrant be $$T(x_T,y_T)$$.
Since $$O$$ and $$R$$ both lie on the $$x$$-axis, the area of $$\triangle ORT$$ equals

$$\text{Area}=\frac12\,(OR)\,\bigl|y_T\bigr| = \frac12\,(3)\,\bigl|y_T\bigr|.$$

Given $$\text{Area}= \frac32,$$ we get
$$\frac12\,(3)\,\bigl|y_T\bigr|=\frac32 \;\Longrightarrow\; |y_T|=1.$$ Because $$T$$ is in the fourth quadrant, $$y_T=-1$$.

Substituting $$y_T=-1$$ in the ellipse,

$$\frac{x_T^{2}}{9}+\frac{(-1)^{2}}{4}=1 \;\Longrightarrow\; \frac{x_T^{2}}{9}+\frac14=1 \;\Longrightarrow\; \frac{x_T^{2}}{9}=\frac34 \;\Longrightarrow\; x_T^{2}=\frac{27}{4} \;\Longrightarrow\; x_T=\frac{3\sqrt3}{2}\;(\text{positive in quadrant IV}).$$

Thus $$T\Bigl(\dfrac{3\sqrt3}{2},\,-1\Bigr).$$

Equation of the two tangents
For a point $$(x_1,y_1)$$ on the ellipse, the tangent is $$\frac{xx_1}{9}+\frac{yy_1}{4}=1.$$

• At the upper end of the minor axis $$(0,2):$$ $$\frac{x\cdot0}{9}+\frac{y\cdot2}{4}=1\;\Longrightarrow\;y=2.$$
• At $$T\Bigl(\dfrac{3\sqrt3}{2},-1\Bigr):$$ $$\frac{x\left(\dfrac{3\sqrt3}{2}\right)}{9}+\frac{y(-1)}{4}=1 \;\Longrightarrow\; \frac{x\sqrt3}{6}-\frac{y}{4}=1 \;\Longrightarrow\; y=\frac{2\sqrt3}{3}\,x-4.$$

Both tangents meet at the external point $$S(p,q)$$, so $$S$$ is the intersection of

$$y=2 \quad\text{and}\quad y=\frac{2\sqrt3}{3}\,x-4.$$

Putting $$y=2$$ in the second equation:

$$2=\frac{2\sqrt3}{3}\,x-4 \;\Longrightarrow\; \frac{2\sqrt3}{3}\,x=6 \;\Longrightarrow\; x=\frac{6\cdot3}{2\sqrt3}=3\sqrt3.$$

Hence $$S(3\sqrt3,\,2).$$

Verification that $$S$$ lies outside the ellipse

$$\frac{p^{2}}{9}+\frac{q^{2}}{4} =\frac{(3\sqrt3)^{2}}{9}+\frac{2^{2}}{4} =\frac{27}{9}+1=3+1=4\gt1,$$ so $$S$$ is indeed outside the ellipse.

The obtained values match Option A:

Option A which is: $$q = 2,\; p = 3\sqrt{3}$$

Line $$5x + 7y = 50$$: $$A(\alpha,0) \Rightarrow 5\alpha = 50 \Rightarrow \alpha = 10$$. $$B(0,\beta) \Rightarrow 7\beta = 50 \Rightarrow \beta = 50/7$$.

P divides AB in ratio 7:3 internally: $$P = \left(\frac{7(0)+3(10)}{10}, \frac{7(50/7)+3(0)}{10}\right) = (3, 5)$$.

Directrix: $$3x - 25 = 0 \Rightarrow x = 25/3$$. For ellipse $$\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$: directrix $$x = a/e$$.

So $$a/e = 25/3$$. Focus $$S = (ae, 0)$$.

Since the perpendicular from S on x-axis passes through P, the x-coordinate of S = x-coordinate of P = 3

So $$ae = 3$$ From $$a/e = 25/3$$ and $$ae = 3$$: $$a^2 = (a/e)(ae) = (25/3)(3) = 25$$, so $$a = 5$$.

$$e = ae/a = 3/5$$. $$b^2 = a^2(1-e^2) = 25(1-9/25) = 16$$.

Length of latus rectum = $$\frac{2b^2}{a} = \frac{32}{5}$$.

The answer is Option (4): $$\boxed{\frac{32}{5}}$$.

For an ellipse, the semi-minor axis is $$b$$ and the distance between foci is $$2c$$ where $$c = ae$$.

Length of minor axis = $$2b$$. Half the distance between foci = $$\frac{2c}{2} = c = ae$$.

Given: $$2b = ae$$, so $$b = \frac{ae}{2}$$.

Using the relation $$b^2 = a^2(1 - e^2)$$:

$$ \frac{a^2e^2}{4} = a^2(1 - e^2) $$

$$ \frac{e^2}{4} = 1 - e^2 $$

$$ e^2 + \frac{e^2}{4} = 1 \Rightarrow \frac{5e^2}{4} = 1 \Rightarrow e^2 = \frac{4}{5} $$

$$ e = \frac{2}{\sqrt{5}} $$

The answer is Option (4): $$\boxed{\frac{2}{\sqrt{5}}}$$.

Hyperbola: $$\frac{x^2}{16} - \frac{y^2}{9} = 1$$. Here $$a_h = 4, b_h = 3$$.

$$e_1 = \sqrt{1 + \frac{9}{16}} = \sqrt{\frac{25}{16}} = \frac{5}{4}$$

Foci of hyperbola: $$(\pm 5, 0)$$.

Given $$e_1 e_2 = 1$$: $$e_2 = \frac{4}{5}$$.

Ellipse passes through $$(\pm 5, 0)$$:

$$\frac{25}{a^2} = 1 \Rightarrow a^2 = 25, a = 5$$.

$$e_2 = \sqrt{1 - \frac{b^2}{a^2}} = \frac{4}{5}$$

$$\frac{b^2}{25} = 1 - \frac{16}{25} = \frac{9}{25}$$

$$b^2 = 9$$

Ellipse: $$\frac{x^2}{25} + \frac{y^2}{9} = 1$$.

Chord at $$y = 2$$: $$\frac{x^2}{25} + \frac{4}{9} = 1 \Rightarrow \frac{x^2}{25} = \frac{5}{9} \Rightarrow x^2 = \frac{125}{9}$$

$$x = \pm\frac{5\sqrt{5}}{3}$$

Length = $$\frac{10\sqrt{5}}{3}$$.

The answer corresponds to Option (3).

Consider an ellipse $$\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$ with $$a > b$$, eccentricity $$e_1 = \frac{1}{\sqrt{2}}$$, and latus rectum length $$= \sqrt{14}$$. 

Since $$e_1^2 = 1 - \frac{b^2}{a^2}$$, we have $$\frac{1}{2} = 1 - \frac{b^2}{a^2}$$, which gives $$\frac{b^2}{a^2} = \frac{1}{2}$$ and hence $$b^2 = \frac{a^2}{2}$$. 

The length of the latus rectum is $$\frac{2b^2}{a} = \sqrt{14}$$; substituting $$b^2 = \frac{a^2}{2}$$ yields $$\frac{2\cdot (a^2/2)}{a} = a = \sqrt{14}$$. Therefore, $$a = \sqrt{14}$$, $$a^2 = 14$$, and $$b^2 = 7$$.

Now consider the hyperbola $$\frac{x^2}{a^2} - \frac{y^2}{b^2} = 1$$, which becomes $$\frac{x^2}{14} - \frac{y^2}{7} = 1$$ when we use the above values. Its eccentricity satisfies $$e_2^2 = 1 + \frac{b^2}{a^2} = 1 + \frac{7}{14} = 1 + \frac{1}{2} = \frac{3}{2}$$.

The answer is Option C: $$\frac{3}{2}$$.

$$f(x) = x^2 + 9$$, $$g(x) = \frac{x}{x-9}$$.

$$a = f(g(10)) = f\left(\frac{10}{1}\right) = f(10) = 100 + 9 = 109$$.

$$b = g(f(3)) = g(9+9) = g(18) = \frac{18}{18-9} = \frac{18}{9} = 2$$.

Ellipse: $$\frac{x^2}{109} + \frac{y^2}{2} = 1$$. Here $$a^2 = 109 > b^2 = 2$$.

Eccentricity: $$e^2 = 1 - \frac{b^2}{a^2} = 1 - \frac{2}{109} = \frac{107}{109}$$.

Latus rectum: $$l = \frac{2b^2}{a} = \frac{4}{\sqrt{109}}$$. So $$l^2 = \frac{16}{109}$$.

$$8e^2 + l^2 = 8 \cdot \frac{107}{109} + \frac{16}{109} = \frac{856 + 16}{109} = \frac{872}{109} = 8$$.

The correct answer is Option 1: 8.

Let P be a point on the ellipse $$\frac{x^2}{9} + \frac{y^2}{4} = 1$$. Parametrize P using the parametric equations for the ellipse: $$x = 3\cos\theta$$, $$y = 2\sin\theta$$, so P is $$(3\cos\theta, 2\sin\theta)$$.

The line passing through P and parallel to the y-axis has the equation $$x = 3\cos\theta$$. This line intersects the circle $$x^2 + y^2 = 9$$. Substitute $$x = 3\cos\theta$$ into the circle equation:

$$(3\cos\theta)^2 + y^2 = 9$$

$$9\cos^2\theta + y^2 = 9$$

$$y^2 = 9 - 9\cos^2\theta = 9\sin^2\theta$$

$$y = \pm 3|\sin\theta|$$

Since P and Q are on the same side of the x-axis, the y-coordinate of Q must have the same sign as that of P. For P, the y-coordinate is $$2\sin\theta$$, so when $$\sin\theta \geq 0$$, Q has a non-negative y-coordinate, and when $$\sin\theta < 0$$, Q has a negative y-coordinate. In both cases, Q can be taken as $$(3\cos\theta, 3\sin\theta)$$.

Thus, Q is $$(3\cos\theta, 3\sin\theta)$$.

Point R is on PQ such that $$PR : RQ = 4 : 3$$. Since PQ is a vertical line segment (same x-coordinate), R divides PQ in the ratio $$PR : RQ = 4 : 3$$. Using the section formula, if R divides the line segment joining $$P(x_1, y_1)$$ and $$Q(x_2, y_2)$$ in the ratio $$m : n$$, then:

$$R = \left( \frac{m x_2 + n x_1}{m + n}, \frac{m y_2 + n y_1}{m + n} \right)$$

Here, $$m = 4$$, $$n = 3$$, $$P(3\cos\theta, 2\sin\theta)$$, $$Q(3\cos\theta, 3\sin\theta)$$.

The x-coordinate of R is:

$$x_R = \frac{4 \cdot (3\cos\theta) + 3 \cdot (3\cos\theta)}{7} = \frac{12\cos\theta + 9\cos\theta}{7} = \frac{21\cos\theta}{7} = 3\cos\theta$$

The y-coordinate of R is:

$$y_R = \frac{4 \cdot (3\sin\theta) + 3 \cdot (2\sin\theta)}{7} = \frac{12\sin\theta + 6\sin\theta}{7} = \frac{18\sin\theta}{7}$$

So R is $$(3\cos\theta, \frac{18}{7} \sin\theta)$$.

To find the locus of R as $$\theta$$ varies, eliminate $$\theta$$:

Set $$x = 3\cos\theta$$ and $$y = \frac{18}{7} \sin\theta$$. Then:

$$\frac{x}{3} = \cos\theta, \quad \frac{7y}{18} = \sin\theta$$

Squaring and adding:

$$\left( \frac{x}{3} \right)^2 + \left( \frac{7y}{18} \right)^2 = \cos^2\theta + \sin^2\theta = 1$$

$$\frac{x^2}{9} + \frac{49y^2}{324} = 1$$

This is the equation of an ellipse. Rewriting it in standard form $$\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$:

$$\frac{x^2}{9} + \frac{y^2}{\frac{324}{49}} = 1$$

So $$a^2 = 9$$ and $$b^2 = \frac{324}{49}$$. Since $$a^2 > b^2$$ (as $$9 > \frac{324}{49} \approx 6.612$$), the major axis is along the x-axis.

The eccentricity $$e$$ is given by:

$$e = \sqrt{1 - \frac{b^2}{a^2}} = \sqrt{1 - \frac{\frac{324}{49}}{9}} = \sqrt{1 - \frac{324}{49 \times 9}} = \sqrt{1 - \frac{324}{441}}$$

Simplify $$\frac{324}{441}$$:

$$\frac{324 \div 9}{441 \div 9} = \frac{36}{49}$$

So:

$$e = \sqrt{1 - \frac{36}{49}} = \sqrt{\frac{49 - 36}{49}} = \sqrt{\frac{13}{49}} = \frac{\sqrt{13}}{7}$$

The eccentricity is $$\frac{\sqrt{13}}{7}$$, which corresponds to option D.

We need to find $$k$$ from the circle equation, then use it to find the latus rectum of the ellipse, and compute $$2m + n$$. The line is $$2x + 3y - k = 0$$ with $$k > 0$$. Its x-intercept is found by setting $$y = 0$$, which gives $$2x = k \implies x = \frac{k}{2}$$ so point $$A = \left(\frac{k}{2}, 0\right)$$, and its y-intercept by setting $$x = 0$$, which gives $$3y = k \implies y = \frac{k}{3}$$ so $$B = \left(0, \frac{k}{3}\right)$$.

The equation of the circle with AB as diameter follows from the general form for endpoints $$(x_1, y_1)$$ and $$(x_2, y_2)$$: $$(x - x_1)(x - x_2) + (y - y_1)(y - y_2) = 0$$ which becomes $$\left(x - \frac{k}{2}\right)(x - 0) + \left(y - 0\right)\left(y - \frac{k}{3}\right) = 0$$ and simplifies to $$x^2 - \frac{k}{2}x + y^2 - \frac{k}{3}y = 0$$.

Comparing this with the given circle equation $$x^2 + y^2 - 3x - 2y = 0$$ shows that $$\frac{k}{2} = 3$$ and $$\frac{k}{3} = 2$$, both yielding $$k = 6$$.

Substituting $$k = 6$$ into the ellipse equation gives $$x^2 + 9y^2 = 36$$, which may be written as $$\frac{x^2}{36} + \frac{y^2}{4} = 1$$. Here $$a^2 = 36$$ and $$b^2 = 4$$, so $$a = 6$$ and $$b = 2$$. The length of the latus rectum is given by $$\ell = \frac{2b^2}{a} = \frac{2 \times 4}{6} = \frac{8}{6} = \frac{4}{3}$$. Writing the latus rectum as $$\frac{m}{n} = \frac{4}{3}$$ with coprime integers $$m = 4$$ and $$n = 3$$, one finds $$2m + n = 2(4) + 3 = 11$$.

The correct answer is Option (1): 11.

The given hyperbola is $$x^{2}-y^{2}\csc^{2}\theta = 5$$.

Divide by $$5$$ to convert it into the standard form $$\dfrac{x^{2}}{a^{2}}-\dfrac{y^{2}}{b^{2}}=1$$:

$$\frac{x^{2}}{5}-\frac{y^{2}\csc^{2}\theta}{5}=1 \;\;\Longrightarrow\;\; \frac{x^{2}}{5}-\frac{y^{2}}{\,5/\csc^{2}\theta\,}=1.$$

Hence for the hyperbola $$a^{2}=5,\qquad b^{2}= \frac{5}{\csc^{2}\theta}=5\sin^{2}\theta.$$ For a hyperbola $$\frac{x^{2}}{a^{2}}-\frac{y^{2}}{b^{2}}=1,$$ the eccentricity is $$e_{h}=\sqrt{1+\frac{b^{2}}{a^{2}}}.$$

Therefore $$e_{h}= \sqrt{1+\frac{5\sin^{2}\theta}{5}} =\sqrt{1+\sin^{2}\theta}.$$

The given ellipse is $$x^{2}\csc^{2}\theta + y^{2}=5.$$

Divide by $$5$$ to write it as $$\dfrac{x^{2}}{a^{2}}+\dfrac{y^{2}}{b^{2}}=1$$:

$$\frac{x^{2}\csc^{2}\theta}{5} + \frac{y^{2}}{5}=1 \;\;\Longrightarrow\;\; \frac{x^{2}}{\,5\sin^{2}\theta\,}+\frac{y^{2}}{5}=1.$$

Thus for the ellipse $$a^{2}=5\sin^{2}\theta,\qquad b^{2}=5.$$ Since $$b^{2}\gt a^{2},$$ the semi-major axis is $$b=\sqrt{5}.$$

For an ellipse $$\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1\;(b\gt a),$$ the eccentricity is $$e_{e}= \sqrt{1-\frac{a^{2}}{b^{2}}}.$$

Hence $$e_{e}= \sqrt{1-\frac{5\sin^{2}\theta}{5}} =\sqrt{1-\sin^{2}\theta} =\cos\theta.$$

According to the question, $$e_{h}= \sqrt{7}\,e_{e}.$$ Substitute the expressions for $$e_{h}$$ and $$e_{e}$$:

$$\sqrt{1+\sin^{2}\theta}= \sqrt{7}\,\cos\theta.$$

Square both sides:

$$1+\sin^{2}\theta = 7\cos^{2}\theta.$$

Using $$\cos^{2}\theta = 1-\sin^{2}\theta,$$ get an equation in $$s=\sin^{2}\theta$$:

$$1+s = 7(1-s) \;\;\Longrightarrow\;\; 1+s = 7-7s \;\;\Longrightarrow\;\; 8s = 6 \;\;\Longrightarrow\;\; s = \frac{3}{4}.$$

Thus $$\sin^{2}\theta = \frac{3}{4} \;\;\Longrightarrow\;\; \sin\theta = \frac{\sqrt{3}}{2}.$$

For $$0 \lt \theta \lt \frac{\pi}{2},$$ this gives $$\theta = \frac{\pi}{3}.$$

Hence the correct option is Option C: $$\displaystyle \frac{\pi}{3}$$.

Let the given parabola $$P$$ have vertex $$V(2,3)$$ and directrix $$L:2x+y-6=0$$.
Distance from $$V$$ to $$L$$ is $$ p \;=\;\frac{\bigl|2\cdot 2 + 3 -6\bigr|}{\sqrt{2^2+1^2}} \;=\;\frac{1}{\sqrt{5}}. $$

The axis of the parabola is perpendicular to the directrix, so its direction is the unit normal to $$L$$, $$ \mathbf{n}=\frac{(2,1)}{\sqrt{5}}. $$ 

Since the vertex lies in the half-plane $$2x+y-6>0$$, the focus lies in the same half-plane. 

Thus the focus is $$ F \;=\;V + p\,\mathbf{n} =\;(2,3)+\frac{1}{\sqrt{5}}\;\frac{(2,1)}{\sqrt{5}} =\Bigl(2+\tfrac{2}{5},\,3+\tfrac{1}{5}\Bigr) =\Bigl(\tfrac{12}{5},\,\tfrac{16}{5}\Bigr). $$

Next, let the ellipse $$E$$ be $$ \frac{x^2}{a^2}+\frac{y^2}{b^2}=1, \quad a>b, \quad\text{with eccentricity }e=\frac{1}{\sqrt{2}}. $$ 

We have the standard formula for an ellipse, $$ e=\frac{c}{a},\quad c^2=a^2-b^2. $$ Since $$e^2=\tfrac12$$, it follows $$ c^2=a^2\,e^2=\frac{a^2}{2}, \quad b^2=a^2-c^2=a^2-\frac{a^2}{2}=\frac{a^2}{2}. $$

 $$ \frac{x^2}{a^2}+\frac{y^2}{\tfrac{a^2}{2}}=1 \quad\Longrightarrow\quad \frac{x^2}{a^2}+\frac{2y^2}{a^2}=1 \quad\Longrightarrow\quad x^2+2y^2=a^2. $$

Since the focus $$F\bigl(\tfrac{12}{5},\tfrac{16}{5}\bigr)$$ of the parabola lies on this ellipse, substitute into $$x^2+2y^2=a^2$$: $$ \Bigl(\tfrac{12}{5}\Bigr)^2+2\Bigl(\tfrac{16}{5}\Bigr)^2 =\frac{144}{25}+\frac{512}{25} =\frac{656}{25} \;=\;a^2. $$

The length of the latus rectum of the ellipse is given by $$ \ell=\frac{2b^2}{a} =\frac{2\bigl(\tfrac{a^2}{2}\bigr)}{a} =\frac{a^2}{a} =a, $$ so the square of its length is $$ \ell^2=a^2=\frac{656}{25}. $$

For the ellipse $$\frac{x^2}{25} + \frac{y^2}{16} = 1$$, we need the chord with midpoint $$(1, \frac{2}{5})$$.

The equation of the chord with midpoint $$(h, k)$$ is given by $$T = S_1$$:

$$\frac{xh}{25} + \frac{yk}{16} = \frac{h^2}{25} + \frac{k^2}{16}$$

With $$(h, k) = (1, \frac{2}{5})$$:

$$\frac{x}{25} + \frac{2y/5}{16} = \frac{1}{25} + \frac{4/25}{16} = \frac{1}{25} + \frac{1}{100}$$

$$\frac{x}{25} + \frac{y}{40} = \frac{4 + 1}{100} = \frac{1}{20}$$

Multiply by 200:

$$8x + 5y = 10$$

So $$y = \frac{10 - 8x}{5} = 2 - \frac{8x}{5}$$.

Substituting into the ellipse equation:

$$\frac{x^2}{25} + \frac{(2 - 8x/5)^2}{16} = 1$$

$$\frac{x^2}{25} + \frac{4 - 32x/5 + 64x^2/25}{16} = 1$$

$$\frac{x^2}{25} + \frac{1}{4} - \frac{2x}{5} + \frac{4x^2}{25} = 1$$

$$\frac{5x^2}{25} - \frac{2x}{5} + \frac{1}{4} = 1$$

$$\frac{x^2}{5} - \frac{2x}{5} = \frac{3}{4}$$

$$\frac{x^2 - 2x}{5} = \frac{3}{4}$$

$$4(x^2 - 2x) = 15$$

$$4x^2 - 8x - 15 = 0$$

$$x = \frac{8 \pm \sqrt{64 + 240}}{8} = \frac{8 \pm \sqrt{304}}{8}$$

The two x-values: $$x_1 + x_2 = 2$$, $$x_1 x_2 = -\frac{15}{4}$$.

$$(x_1 - x_2)^2 = (x_1 + x_2)^2 - 4x_1x_2 = 4 + 15 = 19$$

The corresponding y-values: $$y = 2 - \frac{8x}{5}$$, so $$y_1 - y_2 = -\frac{8}{5}(x_1 - x_2)$$.

Length of chord:

$$L^2 = (x_1 - x_2)^2 + (y_1 - y_2)^2 = (x_1 - x_2)^2\left(1 + \frac{64}{25}\right) = 19 \times \frac{89}{25} = \frac{1691}{25}$$

$$L = \frac{\sqrt{1691}}{5}$$

The answer is $$\frac{\sqrt{1691}}{5}$$, which corresponds to Option (1).

For the ellipse $$\dfrac{x^2}{a^2}+\dfrac{y^2}{b^2}=1,\; a\gt b$$ the standard facts are

• Distance of each focus from the centre: $$c,\; c^2=a^2-b^2$$
• Length of the latus-rectum: $$L=\dfrac{2b^2}{a}$$

The question gives

$$c=5 \;\; \bigl(\text{foci } (\pm5,0)\bigr), \qquad L=\sqrt{50}$$

Step 1: Use the latus-rectum length.

$$\dfrac{2b^2}{a}= \sqrt{50}\;\; \Longrightarrow\;\; b^2=\dfrac{a\sqrt{50}}{2} \quad -(1)$$

Step 2: Use the focus relation.

$$a^2-b^2=25 \quad -(2)$$

Step 3: Substitute $$b^2$$ from $$(1)$$ into $$(2)$$.

$$a^2-\dfrac{a\sqrt{50}}{2}=25$$

Multiply by $$2$$:

$$2a^2-a\sqrt{50}-50=0$$

Step 4: Solve the quadratic in $$a$$.

Using the quadratic formula, $$a=\dfrac{\sqrt{50}\pm\sqrt{(\sqrt{50})^2-4(2)(-50)}}{4}$$

Discriminant: $$(\sqrt{50})^2-4(2)(-50)=50+400=450$$, so $$\sqrt{450}=3\sqrt{50}$$.

Hence $$a=\dfrac{\sqrt{50}\pm3\sqrt{50}}{4}$$. Since $$a\gt0$$, take the positive sign:

$$a=\sqrt{50}, \qquad\Longrightarrow\qquad a^2=50$$

Step 5: Eccentricity of the hyperbola.

The given hyperbola is $$\dfrac{x^2}{b^2}-\dfrac{y^2}{a^2b^2}=1$$

Compare with the standard form $$\dfrac{x^2}{A^2}-\dfrac{y^2}{B^2}=1$$, where

$$A^2=b^2, \qquad B^2=a^2b^2$$

For a hyperbola, $$e^2=1+\dfrac{B^2}{A^2}$$.

Therefore

$$e_{\text{hyper}}^{\,2}=1+\dfrac{a^2b^2}{b^2}=1+a^2$$

Using $$a^2=50$$, we get

$$e_{\text{hyper}}^{\,2}=1+50=51$$

Thus, the square of the eccentricity of the hyperbola equals $$51$$.

The points common to the circle $$x^{2}+y^{2}=4b\quad -(1)$$ and the ellipse $$\frac{x^{2}}{16}+\frac{y^{2}}{b^{2}}=1\quad -(2)$$ are stated to lie on the pair of straight lines $$y^{2}=3x^{2}\; \Longrightarrow\; y=\pm\sqrt{3}\,x\quad -(3)$$.

Substitute $$y^{2}=3x^{2}$$ from $$(3)$$ in the circle $$(1)$$:

$$x^{2}+3x^{2}=4b\;\Longrightarrow\;4x^{2}=4b\;\Longrightarrow\;x^{2}=b\;\Longrightarrow\;|x|=\sqrt{b}$$.

Using $$(3)$$ again, $$y^{2}=3x^{2}=3b\;\Longrightarrow\;|y|=\sqrt{3b}$$.

Hence the four intersection points are $$\bigl(\pm\sqrt{b},\,\pm\sqrt{3b}\bigr)$$, one in each quadrant.

These points must also satisfy the ellipse $$(2)$$. Substitute $$x^{2}=b,\;y^{2}=3b$$ in $$(2)$$:

$$\frac{b}{16}+\frac{3b}{b^{2}}=1 \;\Longrightarrow\;\frac{b}{16}+\frac{3}{b}=1 \;\Longrightarrow\;b^{2}-16b+48=0 \;\Longrightarrow\;(b-12)(b-4)=0$$.

This gives $$b=12$$ or $$b=4$$. When $$b=4$$ the ellipse becomes $$\dfrac{x^{2}}{16}+\dfrac{y^{2}}{16}=1 \;\Longrightarrow\;x^{2}+y^{2}=16$$, identical to the circle. The problem states the conics are distinct, so we reject $$b=4$$ and take $$b=12$$.

Width of the rectangle formed by the four points: $$2|x|=2\sqrt{b}=2\sqrt{12}=4\sqrt{3}$$.
Height of the rectangle: $$2|y|=2\sqrt{3b}=2\sqrt{36}=12$$.

Area of the rectangle $$=4\sqrt{3}\times12=48\sqrt{3}$$.

Required expression: $$3\sqrt{3}\times(\text{area})=3\sqrt{3}\times48\sqrt{3}=3\sqrt{3}\times48\sqrt{3}=3\times48\times3=432$$.

Hence, $$3\sqrt{3}$$ times the required area equals $$432$$.

The two given curves are
ellipse $$E:\dfrac{x^{2}}{6}+\dfrac{y^{2}}{3}=1$$ and parabola $$P:y^{2}=12x$$.

Write the parabola in the standard form $$y^{2}=4ax$$.
Since $$12x=4ax$$, we have $$a=3$$.

Common tangent in slope form
  • For $$P:y^{2}=4ax$$ the tangent having slope $$m$$ is $$y=mx+\dfrac{a}{m}=mx+\dfrac{3}{m}\quad -(1)$$
  • For the ellipse $$\dfrac{x^{2}}{6}+\dfrac{y^{2}}{3}=1$$ the tangent with the same slope $$m$$ is $$y=mx\pm\sqrt{6m^{2}+3}\quad -(2)$$

Because the line must be tangent to both curves, the two intercepts in (1) and (2) must coincide:
$$\dfrac{3}{m}=\pm\sqrt{6m^{2}+3}$$ Square both sides:

$$\left(\dfrac{3}{m}\right)^{2}=6m^{2}+3 \;\Longrightarrow\;9=6m^{4}+3m^{2} \;\Longrightarrow\;6m^{4}+3m^{2}-9=0$$ Divide by $$3$$, put $$n=m^{2}\ge 0$$:

$$2n^{2}+n-3=0 \;\Longrightarrow\;n=\dfrac{-1\pm5}{4}$$ The non-negative root is $$n=1\;\Rightarrow\;m^{2}=1$$, hence $$m=1\quad\text{or}\quad m=-1$$.

Equations of the two common tangents
For $$m=1$$: from (1) $$y=x+3$$   (call this $$T_{1}$$)
For $$m=-1$$: from (1) $$y=-x-3$$ (call this $$T_{2}$$)

Intersection with the x-axis
Set $$y=0$$:
For $$T_{1}$$: $$0=x+3\;\Rightarrow\;(-3,0)$$
For $$T_{2}$$: $$0=-x-3\;\Rightarrow\;(-3,0)$$
Thus both tangents meet the x-axis at the single point $$(-3,0)$$.

Points of contact on the parabola
For $$y^{2}=4ax$$ the tangent $$y=mx+\dfrac{a}{m}$$ touches the curve at $$\left(\dfrac{a}{m^{2}},\dfrac{2a}{m}\right)$$.

• For $$m=1$$: $$A_{1}\bigl(\,3,\,6\bigr)$$
• For $$m=-1$$: $$A_{4}\bigl(\,3,\,-6\bigr)$$

Points of contact on the ellipse
Substitute each tangent in the ellipse and use the fact that a tangent cuts the curve at a repeated root.

For $$T_{1}:y=x+3$$:
$$\dfrac{x^{2}}{6}+\dfrac{(x+3)^{2}}{3}=1 \;\Longrightarrow\;(x+2)^{2}=0 \;\Rightarrow\;x=-2,\;y=1$$ Hence $$A_{2}(-2,1)$$.

For $$T_{2}:y=-x-3$$:
$$\dfrac{x^{2}}{6}+\dfrac{(-x-3)^{2}}{3}=1 \;\Longrightarrow\;(x+2)^{2}=0 \;\Rightarrow\;x=-2,\;y=-1$$ Hence $$A_{3}(-2,-1)$$.

Therefore the four vertices are $$A_{1}(3,6),\;A_{2}(-2,1),\;A_{3}(-2,-1),\;A_{4}(3,-6).$$

Area of quadrilateral $$A_{1}A_{2}A_{3}A_{4}$$ (shoelace formula)

$$$ \begin{array}{r|r} x & y \\ \hline 3 & 6 \\ -2 & 1 \\ -2 & -1 \\ 3 & -6 \\ \end{array} $$$ Sum_{1}=3$$\cdot$$1+(-2)(-1)+(-2)(-6)+3$$\cdot$$6=35\\ Sum_{2}=6(-2)+1(-2)+(-1)3+(-6)3=-35 \]

$$\text{Area}=\dfrac{1}{2}\,\bigl|\,\text{Sum}_{1}-\text{Sum}_{2}\bigr| =\dfrac{1}{2}\,(35-(-35))=\dfrac{70}{2}=35\text{ square units}.$$

Verification of the statements
A. Area is $$35$$ - TRUE.
B. Area is $$36$$ - FALSE.
C. Both tangents meet the x-axis at $$(-3,0)$$ - TRUE.
D. Meeting point $$(-6,0)$$ - FALSE.

Hence the correct options are:
Option A (area $$35$$ square units) and Option C (intersection point $$(-3,0)$$).

To find the eccentricity of the ellipse, we use the equation of the normal to the ellipse and find its maximum distance from the origin.

The given ellipse is:

$$\frac{x^2}{4} + \frac{y^2}{b^2} = 1$$

Here, the semi-major axis is $$a = 2$$ and the semi-minor axis is $$b$$ (since $$b < 2$$).

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Step 1: Write the equation of the normal to the ellipse

The equation of the normal to the ellipse $$\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$ at any parametric point $$(a\cos\theta, b\sin\theta)$$ is:

$$ax\sec\theta - by\cosec\theta = a^2 - b^2$$

Substituting $$a = 2$$ into the equation gives:

$$2x\sec\theta - by\cosec\theta = 4 - b^2$$

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Step 2: Find the distance of the normal from the origin

The perpendicular distance $$p$$ of a line $$Ax + By + C = 0$$ from the origin $$(0,0)$$ is given by the formula:

$$p = \frac{|C|}{\sqrt{A^2 + B^2}}$$

Applying this formula to our normal line:

$$p = \frac{4 - b^2}{\sqrt{4\sec^2\theta + b^2\cosec^2\theta}}$$

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Step 3: Maximize the distance from the origin

To maximize the distance $$p$$, we need to minimize the expression in the denominator:

$$f(\theta) = 4\sec^2\theta + b^2\cosec^2\theta$$

Using the identity $$\sec^2\theta = 1 + \tan^2\theta$$ and $$\cosec^2\theta = 1 + \cot^2\theta$$:

$$f(\theta) = 4(1 + \tan^2\theta) + b^2(1 + \cot^2\theta) = 4 + b^2 + 4\tan^2\theta + b^2\cot^2\theta$$

By applying the Arithmetic Mean-Geometric Mean (AM-GM) inequality on the variable terms:

$$4\tan^2\theta + b^2\cot^2\theta \ge 2\sqrt{4\tan^2\theta \cdot b^2\cot^2\theta} = 4b$$

Thus, the minimum value of the denominator's function is:

$$f(\theta)_{\text{min}} = 4 + b^2 + 4b = (2 + b)^2$$

Substituting this back into the expression for $$p$$ gives the maximum distance:

$$p_{\text{max}} = \frac{4 - b^2}{\sqrt{(2 + b)^2}} = \frac{4 - b^2}{2 + b} = 2 - b$$

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Step 4: Solve for $$b$$ and find the eccentricity $$e$$

We are given that the maximum distance of the normal from the origin is 1:

$$2 - b = 1 \implies b = 1$$

Now, using the standard relationship for the eccentricity $$e$$ of an ellipse:

$$b^2 = a^2(1 - e^2)$$

Substituting $$a = 2$$ and $$b = 1$$:

$$1^2 = 2^2(1 - e^2)$$

$$1 = 4(1 - e^2)$$

$$1 - e^2 = \frac{1}{4} \implies e^2 = \frac{3}{4} \implies e = \frac{\sqrt{3}}{2}$$

Therefore, the eccentricity of the ellipse is equal to $$\frac{\sqrt{3}}{2}$$.

The ellipse $$E_k: kx^2 + k^2y^2 = 1$$ can be written as:

$$\frac{x^2}{1/k} + \frac{y^2}{1/k^2} = 1$$

So semi-major axis $$a = \frac{1}{\sqrt{k}}$$ and semi-minor axis $$b = \frac{1}{k}$$.

The four chords join the endpoints of the major axis $$(±a, 0)$$ and the minor axis $$(0, ±b)$$, forming a rhombus.

The radius of the inscribed circle of this rhombus is:

$$r_k = \frac{ab}{\sqrt{a^2 + b^2}}$$

$$r_k = \frac{\frac{1}{\sqrt{k}} \cdot \frac{1}{k}}{\sqrt{\frac{1}{k} + \frac{1}{k^2}}} = \frac{\frac{1}{k^{3/2}}}{\sqrt{\frac{k+1}{k^2}}} = \frac{\frac{1}{k^{3/2}}}{\frac{\sqrt{k+1}}{k}} = \frac{1}{\sqrt{k}\sqrt{k+1}} = \frac{1}{\sqrt{k(k+1)}}$$

Therefore:

$$\frac{1}{r_k^2} = k(k+1)$$

$$\sum_{k=1}^{20} \frac{1}{r_k^2} = \sum_{k=1}^{20} k(k+1) = \sum_{k=1}^{20} (k^2 + k)$$

$$= \frac{20 \times 21 \times 41}{6} + \frac{20 \times 21}{2} = 2870 + 210 = 3080$$

Ellipse: $$x^2 + 9y^2 = 9$$, i.e., $$\frac{x^2}{9} + y^2 = 1$$.

Semi-major axis $$a = 3$$ (along x), semi-minor axis $$b = 1$$ (along y).

A = positive x-axis intersection = (3, 0). B = positive y-axis = (0, 1).

Circle C has major axis (length 6) as diameter: centre (0,0), radius 3. So $$C: x^2 + y^2 = 9$$.

Line through A(3,0) and B(0,1): $$\frac{x}{3} + y = 1$$ or $$x + 3y = 3$$.

Find intersection of $$x + 3y = 3$$ with $$x^2 + y^2 = 9$$:

$$x = 3 - 3y$$. Substituting: $$(3-3y)^2 + y^2 = 9$$

$$9 - 18y + 9y^2 + y^2 = 9$$

$$10y^2 - 18y = 0$$

$$y(10y - 18) = 0$$

$$y = 0$$ (point A) or $$y = 9/5$$

At $$y = 9/5$$: $$x = 3 - 27/5 = -12/5$$. So $$P = (-12/5, 9/5)$$.

Area of triangle OAP with O(0,0), A(3,0), P(-12/5, 9/5):

$$= \frac{1}{2}|x_A \cdot y_P - x_P \cdot y_A| = \frac{1}{2}|3 \cdot 9/5 - (-12/5) \cdot 0| = \frac{1}{2} \cdot \frac{27}{5} = \frac{27}{10}$$

$$m = 27, n = 10$$. Check coprime: gcd(27,10) = 1 ✓

$$m - n = 27 - 10 = 17$$

The correct answer is Option 3: 17.

1. Simplify the Ellipse Equation

The given equation is $$15x^2 + 19y^2 = 285$$. Divide the entire equation by $$285$$ to bring it into standard form:

$$\frac{x^2}{19} + \frac{y^2}{15} = 1$$

• Semi-major axis squared ($$a^2$$): $$19$$
• Semi-minor axis squared ($$b^2$$): $$15$$
• The minor axis of this ellipse lies along the y-axis.

2. Identify the Circle Equation

The circle is concentric with the ellipse (centered at $$(0,0)$$) and has a radius of $$4$$:

$$x^2 + y^2 = 16 \implies r^2 = 16$$

3. Set the Condition for Common Tangents

A line $$y = mx + c$$ is tangent to:

• The ellipse if $$c^2 = a^2m^2 + b^2$$
• The circle if $$c^2 = r^2(1 + m^2)$$

Equating the two expressions for $$c^2$$:

$$19m^2 + 15 = 16(1 + m^2)$$

$$19m^2 + 15 = 16 + 16m^2$$

$$3m^2 = 1 \implies m = \pm\frac{1}{\sqrt{3}}$$

4. Determine the Angle of Inclination

The slope $$m$$ represents the tangent of the angle $$\theta$$ that the line makes with the x-axis:

$$\tan \theta = \frac{1}{\sqrt{3}} \implies \theta = \frac{\pi}{6}$$

The question specifically asks for the angle of inclination to the minor axis (the y-axis):

$$\text{Angle with y-axis} = \frac{\pi}{2} - \theta = \frac{\pi}{2} - \frac{\pi}{6} = \frac{\pi}{3}$$

Correct Option: (A) $$\frac{\pi}{3}$$

The ellipse $$9x^2 + 4y^2 = 36$$ can be written as $$\frac{x^2}{4} + \frac{y^2}{9} = 1$$ so that $$a^2 = 9,\ b^2 = 4$$ with semi-major axis $$a = 3$$ along the y-axis and semi-minor axis $$b = 2$$ along the x-axis. In this setting, PQ and RS denote two diameters passing through the origin that are perpendicular to each other.

First, one may parametrize the points on the ellipse by considering a line through the origin that makes an angle $$\theta$$ with the x-axis and has the equation $$y = x\tan\theta$$. Substituting this into the ellipse equation leads to $$\frac{x^2}{4} + \frac{x^2\tan^2\theta}{9} = 1$$.

Then if $$r$$ represents the distance from the origin to the intersection point, one has $$x = r\cos\theta$$ and $$y = r\sin\theta$$, which transforms the preceding relation into $$\frac{1}{r^2} = \frac{\cos^2\theta}{4} + \frac{\sin^2\theta}{9}$$.

Next, since PQ and RS are diameters, their lengths are given by $$PQ = 2r_1$$ and $$RS = 2r_2$$, where $$r_1$$ and $$r_2$$ are the corresponding radial distances for the directions $$\theta$$ and $$\theta + 90^\circ$$. Therefore, one finds

$$\frac{1}{(PQ)^2} + \frac{1}{(RS)^2} = \frac{1}{4r_1^2} + \frac{1}{4r_2^2} = \frac{1}{4}\Bigl(\frac{1}{r_1^2} + \frac{1}{r_2^2}\Bigr)\,.$$

Moreover, in the direction $$\theta$$ the relationship $$\frac{1}{r_1^2} = \frac{\cos^2\theta}{4} + \frac{\sin^2\theta}{9}$$ holds, while for the perpendicular direction $$\theta + 90^\circ$$ it becomes $$\frac{1}{r_2^2} = \frac{\sin^2\theta}{4} + \frac{\cos^2\theta}{9}$$. By adding these two expressions one obtains

$$\frac{1}{r_1^2} + \frac{1}{r_2^2} = \frac{\cos^2\theta + \sin^2\theta}{4} + \frac{\sin^2\theta + \cos^2\theta}{9} = \frac{1}{4} + \frac{1}{9} = \frac{13}{36}\,,$$

which is independent of $$\theta$$. Consequently,

$$\frac{1}{(PQ)^2} + \frac{1}{(RS)^2} = \frac{1}{4}\cdot\frac{13}{36} = \frac{13}{144}\,.$$

Since this result is of the form $$\frac{p}{q}$$ with $$p = 13$$ and $$q = 144$$ coprime, their sum is $$p + q = 13 + 144 = 157$$, giving the final answer as \boxed{157}.

Given the ellipse $$x^2 + 4y^2 = 36$$, rewrite as $$\frac{x^2}{36} + \frac{y^2}{9} = 1$$ with $$a^2 = 36, b^2 = 9$$.

We need the largest circle centered at $$(2, 0)$$ inscribed in this ellipse. The circle equation is $$(x - 2)^2 + y^2 = r^2$$.

Substituting $$y^2 = r^2 - (x-2)^2$$ into the ellipse equation:

$$x^2 + 4[r^2 - (x-2)^2] = 36$$

$$x^2 + 4r^2 - 4x^2 + 16x - 16 = 36$$

$$-3x^2 + 16x + 4r^2 - 52 = 0$$

$$3x^2 - 16x + (52 - 4r^2) = 0$$

For the largest inscribed circle, the circle is tangent to the ellipse (touches at exactly one point), so the discriminant equals zero:

$$\Delta = 256 - 12(52 - 4r^2) = 0$$

$$256 - 624 + 48r^2 = 0$$

$$48r^2 = 368$$

$$r^2 = \frac{368}{48} = \frac{23}{3}$$

Therefore:

$$12r^2 = 12 \times \frac{23}{3} = 92$$

The answer is Option B: 92.

Given $$LR = \frac{2b^2}{a} = \frac{1}{2} \implies b^2 = \frac{a}{4}$$

Angle subtended at foci is $$60^\circ \implies \theta = 60^\circ \implies \theta/2 = 30^\circ$$

$$\tan(30^\circ) = \frac{b}{ae} \implies \frac{1}{\sqrt{3}} = \frac{b}{ae} \implies ae = b\sqrt{3}$$

Substitute $$e^2 = 1 - \frac{b^2}{a^2}$$ into $$a^2e^2 = 3b^2$$:

$$a^2\left(1 - \frac{b^2}{a^2}\right) = 3b^2 \implies a^2 - b^2 = 3b^2 \implies a^2 = 4b^2$$

Use $$b^2 = \frac{a}{4}$$:

$$a^2 = 4\left(\frac{a}{4}\right) = a \implies a = 1 \text{ (since } a > 0\text{)}$$

$$b^2 = \frac{1}{4} \implies b = \frac{1}{2}$$

Length of major axis $$= 2a = 2$$; Length of minor axis $$= 2b = 1$$

Sum of axes $$= 2 + 1 = 3$$

Square of the sum $$= 3^2 = 9$$

We are given the ellipse $$E: \frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$ with directrix $$x = 8$$ and corresponding focus $$(2, 0)$$.

First, to determine $$a$$ and $$b$$, recall that for an ellipse the focus is at $$(ae, 0)$$ and the corresponding directrix is at $$x = \frac{a}{e}$$, so we have $$ ae = 2 \quad \text{and} \quad \frac{a}{e} = 8 $$. Multiplying these gives $$a^2 = 16$$, hence $$a = 4$$.

Since $$ae = 2$$, it follows that $$e = \frac{1}{2}$$. Then using $$b^2 = a^2(1 - e^2) = 16\left(1 - \frac{1}{4}\right) = 12$$, the equation of the ellipse becomes $$\frac{x^2}{16} + \frac{y^2}{12} = 1$$.

Next, to find the point $$P$$ in the first quadrant, note that the equation of the tangent to the ellipse at $$P(x_0, y_0)$$ is $$ \frac{x \cdot x_0}{16} + \frac{y \cdot y_0}{12} = 1 $$ and it passes through $$(0, 4\sqrt{3})$$. Substituting yields $$ \frac{0}{16} + \frac{4\sqrt{3} \cdot y_0}{12} = 1 $$, so $$ y_0 = \frac{12}{4\sqrt{3}} = \frac{3}{\sqrt{3}} = \sqrt{3} $$.

Because $$P$$ lies on the ellipse, $$\frac{x_0^2}{16} + \frac{3}{12} = 1 \Rightarrow \frac{x_0^2}{16} = \frac{3}{4} \Rightarrow x_0^2 = 12 \Rightarrow x_0 = 2\sqrt{3}$$, giving $$P = (2\sqrt{3}, \sqrt{3})$$.

To find the x-intercept $$Q$$ of the tangent, set $$y = 0$$ in the tangent equation: $$ \frac{x \cdot 2\sqrt{3}}{16} = 1 \Rightarrow x = \frac{16}{2\sqrt{3}} = \frac{8}{\sqrt{3}} = \frac{8\sqrt{3}}{3} $$. Thus $$Q = \left(\frac{8\sqrt{3}}{3}, 0\right)$$.

Finally, to compute $$(3PQ)^2$$, first evaluate $$ PQ^2 = \left(2\sqrt{3} - \frac{8\sqrt{3}}{3}\right)^2 + (\sqrt{3} - 0)^2 $$ which gives $$ = \left(\frac{6\sqrt{3} - 8\sqrt{3}}{3}\right)^2 + 3 = \left(\frac{-2\sqrt{3}}{3}\right)^2 + 3 $$. Continuing, $$ = \frac{12}{9} + 3 = \frac{4}{3} + 3 = \frac{13}{3} $$. Therefore, $$(3PQ)^2 = 9 \cdot PQ^2 = 9 \times \frac{13}{3} = 39$$.

The hyperbola is $$2x^2 - 2y^2 = 1$$, which can be rewritten as $$\dfrac{x^2}{1/2} - \dfrac{y^2}{1/2} = 1$$.

In this form, $$a_h^2 = b_h^2 = \dfrac{1}{2}$$, so $$c_h^2 = 1$$ and the hyperbola’s eccentricity is $$e_h = \dfrac{c_h}{a_h} = \sqrt{2}$$.

Since the ellipse that meets orthogonally must have eccentricity reciprocal to the hyperbola’s, it follows that $$e = \dfrac{1}{\sqrt{2}}$$.

For an ellipse of the form $$\dfrac{x^2}{a^2} + \dfrac{y^2}{b^2} = 1$$, the eccentricity satisfies $$e^2 = 1 - \frac{b^2}{a^2} = \frac{1}{2} \implies b^2 = \frac{a^2}{2}\,.$$

At a point where this ellipse and the given hyperbola intersect orthogonally, the slope of the ellipse $$y' = -\dfrac{b^2 x}{a^2 y}$$ must be perpendicular to the slope of the hyperbola $$y' = \dfrac{x}{y}$$, which gives $$\left(-\frac{b^2 x}{a^2 y}\right)\left(\frac{x}{y}\right) = -1 \implies \frac{b^2 x^2}{a^2 y^2} = 1 \implies b^2 x^2 = a^2 y^2\,.$$

The hyperbola also satisfies $$y^2 = x^2 - \dfrac{1}{2}$$, and substituting this and $$b^2 = \dfrac{a^2}{2}$$ into $$b^2 x^2 = a^2 y^2$$ yields $$\frac{a^2}{2} x^2 = a^2\left(x^2 - \frac{1}{2}\right) \implies \frac{x^2}{2} = x^2 - \frac{1}{2} \implies x^2 = 1$$ and hence $$y^2 = 1 - \dfrac{1}{2} = \dfrac{1}{2}\,.$$

Since this intersection point lies on the ellipse, substituting $$x^2 = 1$$ and $$y^2 = \tfrac12$$ into $$\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$ gives $$\frac{1}{a^2} + \frac{1/2}{a^2/2} = 1 \implies \frac{1}{a^2} + \frac{1}{a^2} = 1 \implies a^2 = 2$$ and therefore $$b^2 = 1\,.$$

The length of the latus rectum of the ellipse is $$\frac{2b^2}{a} = \frac{2}{\sqrt{2}} = \sqrt{2}$$ so its square is $$(\sqrt{2})^2 = 2\,.$$

Therefore, the answer is $$2$$.

The equation of the curve is:

$$9x^2 + 16y^2 = 144$$

Dividing both sides by $$144$$:

$$\frac{x^2}{16} + \frac{y^2}{9} = 1$$

This is a standard ellipse $$\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$, where:

• $$a^2 = 16 \implies a = 4$$
• $$b^2 = 9 \implies b = 3$$

Step 1: Equation of a Parametric Tangent

Any parametric point on this ellipse can be represented as $$(a \cos\theta, b \sin\theta) = (4 \cos\theta, 3 \sin\theta)$$.

The equation of the tangent to the ellipse at this parametric point is given by:

$$\frac{x \cos\theta}{a} + \frac{y \sin\theta}{b} = 1$$

Substituting $$a = 4$$ and $$b = 3$$:

$$\frac{x \cos\theta}{4} + \frac{y \sin\theta}{3} = 1$$

Step 2: Find the Intercepts $$A$$ and $$B$$

The tangent line intersects the coordinate axes at points $$A$$ (on the x-axis) and $$B$$ (on the y-axis).

• For point $$A$$, set $$y = 0$$:$$\frac{x \cos\theta}{4} = 1 \implies x = \frac{4}{\cos\theta} \implies A = \left(\frac{4}{\cos\theta}, 0\right)$$
• For point $$B$$, set $$x = 0$$:$$\frac{y \sin\theta}{3} = 1 \implies y = \frac{3}{\sin\theta} \implies B = \left(0, \frac{3}{\sin\theta}\right)$$

Step 3: Find the Length of Segment $$AB$$

Using the distance formula, the length $$L$$ of the segment $$AB$$ is:

$$L = \sqrt{\left(\frac{4}{\cos\theta} - 0\right)^2 + \left(0 - \frac{3}{\sin\theta}\right)^2}$$  $$L = \sqrt{\frac{16}{\cos^2\theta} + \frac{9}{\sin^2\theta}}$$

To minimize $$L$$, we can minimize $$L^2$$:

$$f(\theta) = L^2 = 16\sec^2\theta + 9\csc^2\theta$$

Step 4: Minimize $$L^2$$

Using the standard identity $$\sec^2\theta = 1 + \tan^2\theta$$ and $$\csc^2\theta = 1 + \cot^2\theta$$:

$$f(\theta) = 16(1 + \tan^2\theta) + 9(1 + \cot^2\theta)$$  $$f(\theta) = 25 + 16\tan^2\theta + 9\cot^2\theta$$

Using the AM-GM Inequality ($$A \geq G$$) on the variable terms $$16\tan^2\theta$$ and $$9\cot^2\theta$$:

$$\frac{16\tan^2\theta + 9\cot^2\theta}{2} \geq \sqrt{16\tan^2\theta \cdot 9\cot^2\theta}$$  $$16\tan^2\theta + 9\cot^2\theta \geq 2 \cdot \sqrt{144 \cdot (\tan^2\theta \cdot \cot^2\theta)}$$

Since $$\tan^2\theta \cdot \cot^2\theta = 1$$:

$$16\tan^2\theta + 9\cot^2\theta \geq 2 \cdot 12 = 24$$

Substituting this back into our expression for $$f(\theta)$$:

$$f(\theta)_{\text{min}} = 25 + 24 = 49$$

Since $$L^2 \geq 49$$, the minimum length $$L$$ is:

$$L_{\text{min}} = \sqrt{49} = 7$$

Answer:

7

We need to find the largest circle centered at $$(2, 0)$$ inscribed in the ellipse $$\frac{x^2}{36} + \frac{y^2}{16} = 1$$, and then compute $$10\alpha^2$$ given that $$(1, \alpha)$$ lies on this circle.

The equation of the circle is $$(x-2)^2 + y^2 = r^2$$, and for it to be inscribed in the ellipse it must be tangent to the ellipse.

From the ellipse we have $$y^2 = 16\left(1 - \frac{x^2}{36}\right) = \frac{16(36 - x^2)}{36} = \frac{4(36 - x^2)}{9}\,.$$

Substituting this into the circle’s equation gives $$(x-2)^2 + \frac{4(36 - x^2)}{9} = r^2$$ which can be rewritten as $$9(x-2)^2 + 4(36 - x^2) = 9r^2,$$ $$9x^2 - 36x + 36 + 144 - 4x^2 = 9r^2,$$ $$5x^2 - 36x + 180 = 9r^2\,.$$

For the circle to be tangent to the ellipse, the resulting quadratic in $$x$$ must have a double root, so its discriminant is zero: $$5x^2 - 36x + (180 - 9r^2) = 0,$$ $$\Delta = 36^2 - 4(5)(180 - 9r^2) = 0,$$ $$1296 - 20(180 - 9r^2) = 0,$$ $$1296 - 3600 + 180r^2 = 0,$$ $$180r^2 = 2304,$$ $$r^2 = \frac{2304}{180} = \frac{64}{5}\,.$$

Finally, since $$(1, \alpha)$$ lies on the circle $$(x-2)^2 + y^2 = \frac{64}{5}$$, we substitute $$x = 1$$ and $$y = \alpha$$ to get $$(1 - 2)^2 + \alpha^2 = \frac{64}{5},$$ $$1 + \alpha^2 = \frac{64}{5},$$ $$\alpha^2 = \frac{64}{5} - 1 = \frac{59}{5},$$ $$10\alpha^2 = 10 \times \frac{59}{5} = 118\,.$$

The answer is 118.

The ellipse is $$\frac{x^{2}}{4}+\frac{y^{2}}{3}=1$$ with semi-major axis $$a=2$$ and semi-minor axis $$b=\sqrt{3}$$.
Its auxiliary circle has equation $$x^{2}+y^{2}=a^{2}=4$$.

A vertical line through $$H(\alpha,0)\;(0\lt\alpha\lt2)$$ meets

• the ellipse at $$E(\alpha,y_{E})$$, where $$y_{E}=\sqrt{3\!\left(1-\frac{\alpha^{2}}{4}\right)}$$,
• the auxiliary circle at $$F(\alpha,y_{F})$$, where $$y_{F}=\sqrt{4-\alpha^{2}}$$.

The line $$OF$$ makes an angle $$\phi$$ with the positive $$x$$-axis, so

$$\tan\phi=\frac{y_{F}}{\alpha}=\frac{\sqrt{4-\alpha^{2}}}{\alpha}$$.

Squaring gives $$\alpha^{2}\tan^{2}\phi=4-\alpha^{2} \Longrightarrow \alpha^{2}(1+\tan^{2}\phi)=4 \Longrightarrow \alpha^{2}\sec^{2}\phi=4,$$ hence

$$\boxed{\alpha=2\cos\phi} \qquad(0\lt\phi\lt\frac{\pi}{2}).$$

With this, $$y_{F}=\sqrt{4-\alpha^{2}}=2\sin\phi.$$ Thus the segment $$FH$$ has length$$ FH=y_{F}=2\sin\phi.$$ Since $$H$$ and $$G$$ lie on the $$x$$-axis, $$\triangle FGH$$ is right-angled at $$H$$.

The tangent to the ellipse at $$E(\alpha,y_{E})$$ is given by the standard form $$\frac{xx_{1}}{4}+\frac{yy_{1}}{3}=1.$$ Substituting $$(x_{1},y_{1})=(\alpha,y_{E})$$ and putting $$y=0$$ (for the $$x$$-axis) yields $$\frac{x\alpha}{4}=1 \Longrightarrow x=\frac{4}{\alpha}.$$ Hence $$G\!\left(\dfrac{4}{\alpha},0\right)$$ and $$GH=\frac{4}{\alpha}-\alpha=\frac{4-\alpha^{2}}{\alpha} =\frac{4(1-\cos^{2}\phi)}{2\cos\phi} =\frac{2\sin^{2}\phi}{\cos\phi}.$$

The required area is therefore $$ \text{Area}(FGH)=\frac12\,(FH)\,(GH) =\frac12\,(2\sin\phi)\left(\frac{2\sin^{2}\phi}{\cos\phi}\right) =\boxed{\frac{2\sin^{3}\phi}{\cos\phi}}.$$

Combining the results:

(I) $$\to$$ (Q), (II) $$\to$$ (T), (III) $$\to$$ (S), (IV) $$\to$$ (P).

Hence the correct option is
Option C: (I) → (Q); (II) → (T); (III) → (S); (IV) → (P).

We need to find $$12m^2$$ where $$m$$ is the slope of a common tangent to the ellipse $$\frac{x^2}{16} + \frac{y^2}{9} = 1$$ and the circle $$x^2 + y^2 = 12$$.

For the ellipse $$\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$ with $$a^2 = 16$$ and $$b^2 = 9$$, the equation of a tangent line with slope $$m$$ can be written as

$$y = mx \pm \sqrt{a^2 m^2 + b^2} = mx \pm \sqrt{16m^2 + 9}$$

This follows from the condition that a line $$y = mx + c$$ is tangent to the ellipse when $$c^2 = a^2 m^2 + b^2$$.

For the circle $$x^2 + y^2 = 12$$ (with center at the origin and radius $$2\sqrt{3}$$), the tangent line with slope $$m$$ has the form

$$y = mx \pm \sqrt{12(1 + m^2)}$$

This follows from the requirement that the perpendicular distance from the center to the line equals the radius, namely $$\frac{|c|}{\sqrt{1+m^2}} = 2\sqrt{3}$$, which leads to $$c^2 = 12(1+m^2)$$.

For a common tangent, the value of $$c^2$$ must satisfy both conditions simultaneously, so we set

$$16m^2 + 9 = 12(1 + m^2)\,.$$

Rewriting this gives

$$16m^2 + 9 = 12 + 12m^2$$

Subtracting terms yields

$$4m^2 = 3\quad\text{and}\quad m^2 = \frac{3}{4}\,.$$

Substituting into $$12m^2$$ gives

$$12m^2 = 12 \times \frac{3}{4} = 9$$

Therefore, the required value is $$9$$.

The lines $$bx + 10y - 8 = 0$$ and $$2x - 3y = 0$$ intersect where $$x = \dfrac{3y}{2}$$, giving $$\dfrac{3by}{2} + 10y = 8$$, so $$y = \dfrac{16}{3b + 20}$$ and $$x = \dfrac{24}{3b + 20}$$.

Line $$L$$ passes through this intersection point and through $$(1, 1)$$. The equation of $$L$$ can be written as a member of the family:

$$(bx + 10y - 8) + \lambda(2x - 3y) = 0$$

Since $$L$$ passes through $$(1, 1)$$: $$(b + 10 - 8) + \lambda(2 - 3) = 0$$, so $$b + 2 - \lambda = 0$$, giving $$\lambda = b + 2$$.

The equation of $$L$$ becomes: $$(b + 2(b+2))x + (10 - 3(b+2))y - 8 = 0$$

$$= (3b + 4)x + (4 - 3b)y - 8 = 0$$

Line $$L$$ touches the circle $$17(x^2 + y^2) = 16$$, i.e., $$x^2 + y^2 = \dfrac{16}{17}$$. The distance from the center $$(0, 0)$$ to the line equals the radius $$\dfrac{4}{\sqrt{17}}$$.

$$\dfrac{|0 + 0 - 8|}{\sqrt{(3b+4)^2 + (4-3b)^2}} = \dfrac{4}{\sqrt{17}}$$

$$\dfrac{64}{(3b+4)^2 + (4-3b)^2} = \dfrac{16}{17}$$

$$(3b+4)^2 + (4-3b)^2 = 64 \cdot \dfrac{17}{16} = 68$$

Expanding: $$9b^2 + 24b + 16 + 16 - 24b + 9b^2 = 68$$

$$18b^2 + 32 = 68$$, so $$18b^2 = 36$$, giving $$b^2 = 2$$.

The ellipse is $$\dfrac{x^2}{5} + \dfrac{y^2}{b^2} = 1$$ with $$b^2 = 2$$. Since $$b^2 < 5$$, the semi-major axis is along the $$x$$-axis with $$a^2 = 5$$.

The eccentricity is $$e = \sqrt{1 - \dfrac{b^2}{a^2}} = \sqrt{1 - \dfrac{2}{5}} = \sqrt{\dfrac{3}{5}} = \dfrac{\sqrt{3}}{\sqrt{5}}$$.

The correct answer is Option B: $$\dfrac{\sqrt{3}}{\sqrt{5}}$$.

We are given an ellipse $$\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$ with $$a > b$$ and eccentricity $$e = \frac{1}{4}$$. For such an ellipse, the eccentricity satisfies

$$e^2 = 1 - \frac{b^2}{a^2}$$

so

$$\frac{1}{16} = 1 - \frac{b^2}{a^2},$$

which implies

$$\frac{b^2}{a^2} = 1 - \frac{1}{16} = \frac{15}{16},$$

and hence

$$b^2 = \frac{15a^2}{16}.$$

The ellipse also passes through the point $$\left(-4\sqrt{\frac{2}{5}},\;3\right)$$. Substituting this into the equation of the ellipse gives

$$\frac{\left(-4\sqrt{\frac{2}{5}}\right)^2}{a^2} + \frac{3^2}{b^2} = 1,$$

which simplifies to

$$\frac{16 \times \frac{2}{5}}{a^2} + \frac{9}{b^2} = 1$$

and therefore

$$\frac{32}{5a^2} + \frac{9}{b^2} = 1.$$

Next, substituting $$b^2 = \frac{15a^2}{16}$$ into this equation yields

$$\frac{32}{5a^2} + \frac{9 \times 16}{15a^2} = 1,$$

or

$$\frac{32}{5a^2} + \frac{144}{15a^2} = 1.$$

Since $$\frac{144}{15} = \frac{48}{5},$$ this becomes

$$\frac{32}{5a^2} + \frac{48}{5a^2} = 1,$$

so

$$\frac{80}{5a^2} = 1 \quad\Longrightarrow\quad \frac{16}{a^2} = 1 \quad\Longrightarrow\quad a^2 = 16.$$

Substituting back to find $$b^2$$ gives

$$b^2 = \frac{15 \times 16}{16} = 15.$$

Finally,

$$a^2 + b^2 = 16 + 15 = 31.$$

The correct answer is Option B: $$31$$.

The ellipse is $$\frac{x^2}{a^2} + \frac{y^2}{4} = 1$$ with $$a > 2$$, so the major axis is along the x-axis with semi-major axis $$a$$ and semi-minor axis $$b = 2$$. One vertex of the triangle is at one end of the major axis, say $$(a, 0)$$, and the other two vertices lie on the vertical line $$x = t$$.

From the ellipse equation at $$x = t$$ one gets $$y = \pm 2\sqrt{1 - \frac{t^2}{a^2}}$$. The area of the triangle with vertices $$(a, 0)$$, $$(t, y_0)$$, $$(t, -y_0)$$ is $$A = \frac{1}{2}|a - t|\times 2y_0 = (a - t)\times 2\sqrt{1 - \frac{t^2}{a^2}}$$. Let $$u = \frac{t}{a}$$, so $$A = 2a(1 - u)\sqrt{1 - u^2}$$.

We maximize $$A^2 = 4a^2(1-u)^2(1-u^2) = 4a^2(1-u)^3(1+u)$$. Let $$f(u) = (1-u)^3(1+u)$$; setting $$f'(u) = 0$$ gives

$$f'(u) = -3(1-u)^2(1+u) + (1-u)^3 = (1-u)^2[-3(1+u) + (1-u)] = (1-u)^2(-2 - 4u) = 0$$

Hence $$u = -\frac{1}{2}$$ (since $$u \neq 1$$), meaning $$t = -\frac{a}{2}$$. Computing the maximum area at $$u = -\frac{1}{2}$$ yields

$$f\left(-\frac{1}{2}\right) = \left(\frac{3}{2}\right)^3 \times \frac{1}{2} = \frac{27}{16},\quad A_{\max}^2 = 4a^2 \times \frac{27}{16} = \frac{27a^2}{4},\quad A_{\max} = \frac{3a\sqrt{3}}{2}$$.

Setting $$A_{\max} = 6\sqrt{3}$$ gives

$$\frac{3a\sqrt{3}}{2} = 6\sqrt{3} \implies a = 4$$.

Calculating the eccentricity: $$e = \sqrt{1 - \frac{b^2}{a^2}} = \sqrt{1 - \frac{4}{16}} = \sqrt{\frac{3}{4}} = \frac{\sqrt{3}}{2}$$.

Therefore, the eccentricity is Option A: $$\frac{\sqrt{3}}{2}$$.

We need to find the acute angle between the pair of tangents drawn to the ellipse $$2x^2 + 3y^2 = 5$$ from the point $$(1, 3)$$.

$$\frac{x^2}{5/2} + \frac{y^2}{5/3} = 1$$

Here $$a^2 = \frac{5}{2}$$ and $$b^2 = \frac{5}{3}$$.

The tangent to the ellipse $$\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$ with slope $$m$$ is:

$$y = mx \pm \sqrt{a^2m^2 + b^2}$$

$$y = mx \pm \sqrt{\frac{5m^2}{2} + \frac{5}{3}}$$

$$3 = m \pm \sqrt{\frac{5m^2}{2} + \frac{5}{3}}$$

$$(3 - m)^2 = \frac{5m^2}{2} + \frac{5}{3}$$

$$9 - 6m + m^2 = \frac{5m^2}{2} + \frac{5}{3}$$

Multiply through by 6:

$$54 - 36m + 6m^2 = 15m^2 + 10$$

$$9m^2 + 36m - 44 = 0$$

$$m_1 + m_2 = -\frac{36}{9} = -4$$

$$m_1 m_2 = -\frac{44}{9}$$

$$\tan\theta = \left|\frac{m_1 - m_2}{1 + m_1 m_2}\right|$$

First, find $$|m_1 - m_2|$$:

$$(m_1 - m_2)^2 = (m_1 + m_2)^2 - 4m_1m_2 = 16 + \frac{176}{9} = \frac{144 + 176}{9} = \frac{320}{9}$$

$$|m_1 - m_2| = \frac{\sqrt{320}}{3} = \frac{8\sqrt{5}}{3}$$

Next, find $$1 + m_1m_2$$:

$$1 + m_1m_2 = 1 - \frac{44}{9} = -\frac{35}{9}$$

Therefore:

$$\tan\theta = \left|\frac{8\sqrt{5}/3}{-35/9}\right| = \frac{8\sqrt{5}}{3} \times \frac{9}{35} = \frac{72\sqrt{5}}{105} = \frac{24\sqrt{5}}{35} = \frac{24}{7\sqrt{5}}$$

So $$\theta = \tan^{-1}\left(\frac{24}{7\sqrt{5}}\right)$$.

Therefore, the correct answer is Option B: $$\tan^{-1}\dfrac{24}{7\sqrt{5}}$$.

We need to find the eccentricity of the ellipse $$\dfrac{x^2}{a^2} + \dfrac{y^2}{b^2} = 1$$. First we determine where the line $$\dfrac{x}{7} + \dfrac{y}{2\sqrt{6}} = 1$$ meets the $$x$$-axis by setting $$y = 0$$, which reduces to

$$

\dfrac{x}{7} = 1 \implies x = 7

$$

Therefore the ellipse passes through $$(7, 0)$$. Substituting these coordinates into the ellipse equation gives

$$

\dfrac{49}{a^2} = 1 \implies a^2 = 49, \quad a = 7

$$

Next, to find where the line $$\dfrac{x}{7} - \dfrac{y}{2\sqrt{6}} = 1$$ meets the $$y$$-axis, we set $$x = 0$$, yielding

$$

-\dfrac{y}{2\sqrt{6}} = 1 \implies y = -2\sqrt{6}

$$

This means the ellipse passes through $$(0, -2\sqrt{6})$$. Substituting this point into the ellipse equation gives

$$

\dfrac{24}{b^2} = 1 \implies b^2 = 24

$$

Since $$a^2 = 49 > b^2 = 24$$, the major axis lies along the $$x$$-axis. Hence the eccentricity is

$$

e = \sqrt{1 - \dfrac{b^2}{a^2}} = \sqrt{1 - \dfrac{24}{49}} = \sqrt{\dfrac{25}{49}} = \dfrac{5}{7}

$$

The correct answer is Option A: $$\dfrac{5}{7}$$.

We need to find the intersection of the line $$y = x + 1$$ with the ellipse $$\frac{x^2}{4} + \frac{y^2}{2} = 1$$, then find $$PQ$$ as a diameter of a circle with radius $$r$$, and compute $$(3r)^2$$.

Step 1: Find the intersection points.

Substituting $$y = x + 1$$ into the ellipse equation:

$$\frac{x^2}{4} + \frac{(x+1)^2}{2} = 1$$

$$\frac{x^2}{4} + \frac{x^2 + 2x + 1}{2} = 1$$

Multiplying through by 4:

$$x^2 + 2(x^2 + 2x + 1) = 4$$

$$x^2 + 2x^2 + 4x + 2 = 4$$

$$3x^2 + 4x - 2 = 0$$

Step 2: Use Vieta's formulas.

Let the roots be $$x_1$$ and $$x_2$$. By Vieta's formulas:

$$x_1 + x_2 = -\frac{4}{3}$$ $$-(1)$$

$$x_1 x_2 = -\frac{2}{3}$$ $$-(2)$$

Step 3: Compute $$|PQ|^2$$.

Since both points lie on $$y = x + 1$$, we have $$P = (x_1, x_1 + 1)$$ and $$Q = (x_2, x_2 + 1)$$.

$$|PQ|^2 = (x_1 - x_2)^2 + (y_1 - y_2)^2 = (x_1 - x_2)^2 + (x_1 - x_2)^2 = 2(x_1 - x_2)^2$$

Now: $$(x_1 - x_2)^2 = (x_1 + x_2)^2 - 4x_1 x_2 = \frac{16}{9} + \frac{8}{3} = \frac{16}{9} + \frac{24}{9} = \frac{40}{9}$$

So: $$|PQ|^2 = 2 \times \frac{40}{9} = \frac{80}{9}$$

Step 4: Find the radius.

Since $$PQ$$ is the diameter of the circle: $$|PQ| = 2r$$, so $$|PQ|^2 = 4r^2$$.

$$4r^2 = \frac{80}{9}$$

$$r^2 = \frac{80}{36} = \frac{20}{9}$$

Step 5: Compute $$(3r)^2$$.

$$(3r)^2 = 9r^2 = 9 \times \frac{20}{9} = 20$$

The answer is $$20$$, which matches Option A.

We need to find $$|2x_1 + x_2|$$ where a common tangent T (not passing through the fourth quadrant) touches the ellipse $$C_1: \frac{x^2}{4} + \frac{y^2}{9} = 1$$ at $$(x_1, y_1)$$ and the hyperbola $$C_2: \frac{x^2}{42} - \frac{y^2}{143} = 1$$ at $$(x_2, y_2)$$.

For the ellipse $$\frac{x^2}{4} + \frac{y^2}{9} = 1$$ (here $$a^2 = 4, b^2 = 9$$), the equation of the tangent in slope-intercept form is $$y = mx \pm \sqrt{4m^2 + 9}$$.

Similarly, for the hyperbola $$\frac{x^2}{42} - \frac{y^2}{143} = 1$$ (here $$a^2 = 42, b^2 = 143$$), we have $$y = mx \pm \sqrt{42m^2 - 143}$$.

Since the tangent is common, the expressions under the square root must be equal, which yields $$4m^2 + 9 = 42m^2 - 143$$. Solving gives $$38m^2 = 152$$, so $$m^2 = 4$$ and $$m = \pm 2$$.

Substituting $$m^2 = 4$$ into $$c^2 = 4m^2 + 9$$ leads to $$c^2 = 25$$ and hence $$c = \pm 5$$.

Therefore, the four candidate tangents are $$y = 2x + 5$$, $$y = 2x - 5$$, $$y = -2x + 5$$, and $$y = -2x - 5$$.

To ensure the line does not enter the fourth quadrant ($$x > 0, y < 0$$), we require that $$y \ge 0$$ whenever $$x > 0$$. In this context, for $$y = 2x + 5$$, we have $$y > 5$$ for all $$x > 0$$, so the line always lies above the x-axis.

Next, recall that the point of tangency $$(x_1, y_1)$$ on the ellipse $$\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$ for a line $$y = mx + c$$ is given by $$\left(-\frac{a^2 m}{c}, \frac{b^2}{c}\right)$$.

With $$a^2 = 4$$, $$b^2 = 9$$, $$m = 2$$, and $$c = 5$$, it follows that $$x_1 = -\frac{4 \times 2}{5} = -\frac{8}{5}$$ and $$y_1 = \frac{9}{5}$$.

Verification: $$\frac{(-8/5)^2}{4} + \frac{(9/5)^2}{9} = \frac{64/25}{4} + \frac{81/25}{9} = \frac{16}{25} + \frac{9}{25} = 1$$, confirming the point lies on $$C_1$$.

Similarly, for the hyperbola $$\frac{x^2}{a^2} - \frac{y^2}{b^2} = 1$$, the tangency point for $$y = mx + c$$ is given by $$\left(-\frac{a^2 m}{c}, -\frac{b^2}{c}\right)$$.

With $$a^2 = 42$$, $$b^2 = 143$$, $$m = 2$$, and $$c = 5$$, we find $$x_2 = -\frac{42 \times 2}{5} = -\frac{84}{5}$$ and $$y_2 = -\frac{143}{5}$$.

Verification: $$\frac{(-84/5)^2}{42} - \frac{(-143/5)^2}{143} = \frac{7056/25}{42} - \frac{20449/25}{143} = \frac{168}{25} - \frac{143}{25} = \frac{25}{25} = 1$$, confirming the point lies on $$C_2$$.

Additionally, substituting $$x_2$$ into $$y = 2x + 5$$ gives $$y_2 = 2\left(-\frac{84}{5}\right) + 5 = -\frac{168}{5} + \frac{25}{5} = -\frac{143}{5}$$, verifying consistency with the tangent line.

Finally, we compute $$2x_1 + x_2 = 2\left(-\frac{8}{5}\right) + \left(-\frac{84}{5}\right) = -\frac{16}{5} - \frac{84}{5} = -\frac{100}{5} = -20$$, and hence $$|2x_1 + x_2| = 20$$.

Therefore, the required value is $$\boxed{20}$$.

Let $$f(x) = ax^2 + bx + c$$. We are given $$f(1) = 3$$, $$f(-2) = \lambda$$, $$f(3) = 4$$, and $$f(0) + f(1) + f(-2) + f(3) = 14$$.

From $$f(0) = c$$, the sum condition gives $$c + 3 + \lambda + 4 = 14$$, so $$c + \lambda = 7$$ $$-(1)$$.

From $$f(1) = a + b + c = 3$$ $$-(2)$$.

From $$f(3) = 9a + 3b + c = 4$$ $$-(3)$$.

Subtracting $$(2)$$ from $$(3)$$: $$8a + 2b = 1$$ $$-(4)$$.

From $$f(-2) = 4a - 2b + c = \lambda$$ $$-(5)$$.

From $$(1)$$: $$c = 7 - \lambda$$. Substituting into $$(2)$$: $$a + b = 3 - (7 - \lambda) = \lambda - 4$$ $$-(6)$$.

Substituting $$c = 7 - \lambda$$ into $$(5)$$: $$4a - 2b + 7 - \lambda = \lambda$$, so $$4a - 2b = 2\lambda - 7$$ $$-(7)$$.

From $$(6)$$: $$b = \lambda - 4 - a$$. Substituting into $$(4)$$: $$8a + 2(\lambda - 4 - a) = 1$$, so $$6a + 2\lambda - 8 = 1$$, giving $$a = \dfrac{9 - 2\lambda}{6}$$ $$-(8)$$.

From $$(6)$$: $$b = \lambda - 4 - \dfrac{9 - 2\lambda}{6} = \dfrac{6\lambda - 24 - 9 + 2\lambda}{6} = \dfrac{8\lambda - 33}{6}$$.

Substituting into $$(7)$$: $$4 \cdot \dfrac{9-2\lambda}{6} - 2 \cdot \dfrac{8\lambda-33}{6} = 2\lambda - 7$$.

$$\dfrac{36 - 8\lambda - 16\lambda + 66}{6} = 2\lambda - 7$$

$$\dfrac{102 - 24\lambda}{6} = 2\lambda - 7$$

$$102 - 24\lambda = 12\lambda - 42$$

$$144 = 36\lambda$$, so $$\lambda = 4$$.

The answer is $$4$$.

Given hyperbola

$$H:x^2-y^2=1$$

Comparing with

$$\frac{x^2}{a^2}-\frac{y^2}{b^2}=1,$$

we get

$$a^2=1,\qquad b^2=1$$

Hence eccentricity of $$H$$ is

$$e_H=\sqrt{1+\frac{b^2}{a^2}}=\sqrt2$$

Given, eccentricity of ellipse $$E$$ is reciprocal of eccentricity of $$H.$$

Therefore,

$$e_E=\frac1{\sqrt2}$$

For ellipse

$$E:\frac{x^2}{a^2}+\frac{y^2}{b^2}=1,$$

eccentricity is

$$e_E=\sqrt{1-\frac{b^2}{a^2}}$$

Thus,

$$\sqrt{1-\frac{b^2}{a^2}}=\frac1{\sqrt2}$$

Squaring,

$$1-\frac{b^2}{a^2}=\frac12$$

$$\frac{b^2}{a^2}=\frac12$$

$$a^2=2b^2\qquad\cdots(1)$$

Now,

$$y=\sqrt{\frac52}x+K$$

is tangent to both curves.

For hyperbola

$$x^2-y^2=1,$$

the tangent with slope $$m$$ is

$$y=mx\pm\sqrt{m^2-1}$$

Here,

$$m=\sqrt{\frac52}$$

Hence,

$$K^2=m^2-1=\frac52-1=\frac32\qquad\cdots(2)$$

For ellipse

$$\frac{x^2}{a^2}+\frac{y^2}{b^2}=1,$$

the tangent with slope $$m$$ is

$$y=mx\pm\sqrt{a^2m^2+b^2}$$

Therefore,

$$K^2=a^2m^2+b^2$$

Using

$$m^2=\frac52,$$

$$K^2=\frac52a^2+b^2\qquad\cdots(3)$$

From (2) and (3),

$$\frac52a^2+b^2=\frac32$$

Using

$$a^2=2b^2,$$

$$\frac52(2b^2)+b^2=\frac32$$

$$6b^2=\frac32$$

$$b^2=\frac14$$

Hence,

$$a^2=\frac12$$

Therefore,

$$4(a^2+b^2)=4\left(\frac12+\frac14\right)$$

$$=4\cdot\frac34$$

$$=3$$

Hence, the required value is

$$\boxed{3}$$.

We have $$S = \{(x,y) \in \mathbb{N} \times \mathbb{N} : 9(x-3)^2 + 16(y-4)^2 \leq 144\}$$, which represents the natural number lattice points inside or on the ellipse $$\frac{(x-3)^2}{16} + \frac{(y-4)^2}{9} \leq 1$$ centered at $$(3,4)$$ with semi-major axis $$a = 4$$ (horizontal) and semi-minor axis $$b = 3$$ (vertical). The set $$T = \{(x,y) \in \mathbb{R} \times \mathbb{R} : (x-7)^2 + (y-4)^2 \leq 36\}$$ is the disk centered at $$(7,4)$$ with radius 6.

For the ellipse, $$x$$ ranges over $$[-1, 7]$$ and $$y$$ over $$[1, 7]$$. Since we need natural numbers ($$\mathbb{N} = \{1, 2, 3, \ldots\}$$), we consider $$x \in \{1, 2, 3, 4, 5, 6, 7\}$$.

We enumerate the lattice points in the ellipse at each $$x$$-value and check which of them also satisfy the circle condition $$(x-7)^2 + (y-4)^2 \leq 36$$.

At $$x = 1$$: The ellipse gives $$16(y-4)^2 \leq 144 - 36 = 108$$, so $$(y-4)^2 \leq 6.75$$, meaning $$y \in \{2, 3, 4, 5, 6\}$$ (5 lattice points). The circle requires $$(1-7)^2 + (y-4)^2 = 36 + (y-4)^2 \leq 36$$, which forces $$y = 4$$. This gives 1 point in $$S \cap T$$.

At $$x = 2$$: The ellipse gives $$16(y-4)^2 \leq 144 - 9 = 135$$, so $$(y-4)^2 \leq 8.4375$$, meaning $$|y - 4| \leq 2$$ (since $$3^2 = 9 > 8.4375$$). So $$y \in \{2, 3, 4, 5, 6\}$$ (5 lattice points). The circle gives $$(2-7)^2 + (y-4)^2 = 25 + (y-4)^2 \leq 36$$, so $$(y-4)^2 \leq 11$$. All 5 points satisfy this. This gives 5 points.

At $$x = 3$$: The ellipse gives $$(y-4)^2 \leq 9$$, so $$|y-4| \leq 3$$, meaning $$y \in \{1, 2, 3, 4, 5, 6, 7\}$$ (7 points). The circle gives $$16 + (y-4)^2 \leq 36$$, so $$(y-4)^2 \leq 20$$. All 7 qualify. This gives 7 points.

At $$x = 4$$: Same ellipse condition as $$x = 2$$ (since $$(4-3)^2 = (2-3)^2 = 1$$): $$y \in \{2, 3, 4, 5, 6\}$$ (5 points). The circle gives $$9 + (y-4)^2 \leq 36$$, so $$(y-4)^2 \leq 27$$. All 5 qualify. This gives 5 points.

At $$x = 5$$: The ellipse gives $$16(y-4)^2 \leq 144 - 36 = 108$$, so $$(y-4)^2 \leq 6.75$$, meaning $$y \in \{2, 3, 4, 5, 6\}$$ (5 points). The circle gives $$4 + (y-4)^2 \leq 36$$. All 5 qualify. This gives 5 points.

At $$x = 6$$: The ellipse gives $$16(y-4)^2 \leq 144 - 81 = 63$$, so $$(y-4)^2 \leq 3.9375$$, meaning $$|y-4| \leq 1$$, so $$y \in \{3, 4, 5\}$$ (3 points). The circle gives $$1 + (y-4)^2 \leq 36$$. All 3 qualify. This gives 3 points.

At $$x = 7$$: The ellipse gives $$16(y-4)^2 \leq 144 - 144 = 0$$, so $$y = 4$$ (1 point). The circle gives $$0 + 0 \leq 36$$. This gives 1 point.

The total count is $$1 + 5 + 7 + 5 + 5 + 3 + 1 = 27$$.

Hence, the correct answer is $$\boxed{27}$$.

The ellipse $$E: 3x^2 + 4y^2 = 12$$ can be written as $$\frac{x^2}{4} + \frac{y^2}{3} = 1$$.

So $$a_E^2 = 4$$, $$b_E^2 = 3$$. The latus rectum of the ellipse is $$\frac{2b_E^2}{a_E} = \frac{2 \times 3}{2} = 3$$.

The eccentricity of the ellipse: $$e_E^2 = 1 - \frac{b_E^2}{a_E^2} = 1 - \frac{3}{4} = \frac{1}{4}$$.

The hyperbola $$H: \frac{x^2}{a^2} - y^2 = 1$$ has $$b_H = 1$$.

The latus rectum of the hyperbola is $$\frac{2b_H^2}{a} = \frac{2}{a}$$.

Setting the latus rectum of $$H$$ equal to that of $$E$$:

$$\frac{2}{a} = 3$$, so $$a = \frac{2}{3}$$.

The eccentricity of the hyperbola: $$e_H^2 = 1 + \frac{b_H^2}{a^2} = 1 + \frac{1}{4/9} = 1 + \frac{9}{4} = \frac{13}{4}$$.

Therefore:

$$12(e_H^2 + e_E^2) = 12\left(\frac{13}{4} + \frac{1}{4}\right) = 12 \times \frac{14}{4} = 12 \times \frac{7}{2} = 42$$

The correct answer is $$42$$.

We are given that for $$a > b > 0$$ the area of the set $$\{(x,y) : x^2 + y^2 \leq a^2 \text{ and } \frac{x^2}{a^2} + \frac{y^2}{b^2} \geq 1\}$$ is $$30\pi$$ and the area of the set $$\{(x,y) : x^2 + y^2 \geq b^2 \text{ and } \frac{x^2}{a^2} + \frac{y^2}{b^2} \leq 1\}$$ is $$18\pi$$.

The first region, which lies inside the circle of radius $$a$$ but outside the ellipse, has area $$\pi a^2 - \pi ab = \pi a(a - b) = 30\pi$$, giving $$a(a-b) = 30 \quad \cdots(1)$$. Similarly, the second region, which lies inside the ellipse but outside the circle of radius $$b$$, has area $$\pi ab - \pi b^2 = \pi b(a - b) = 18\pi$$, yielding $$b(a-b) = 18 \quad \cdots(2)$$.

On dividing equation (1) by equation (2), we obtain $$\dfrac{a}{b} = \dfrac{30}{18} = \dfrac{5}{3}$$, so $$a = \dfrac{5b}{3}$$. Substituting this into (2) leads to $$b\left(\dfrac{5b}{3} - b\right) = 18$$, hence $$b \cdot \dfrac{2b}{3} = 18 \Rightarrow b^2 = 27$$. It then follows that $$a - b = \dfrac{5b}{3} - b = \dfrac{2b}{3}$$.

Therefore, $$(a-b)^2 = \dfrac{4b^2}{9} = \dfrac{4 \times 27}{9} = \boxed{12}\,.$$

We have the ellipse $$\frac{x^2}{2} + \frac{y^2}{4} = 1$$. Here $$a^2 = 4$$ (along the $$y$$-axis since $$4 > 2$$), $$b^2 = 2$$, so $$c^2 = a^2 - b^2 = 2$$, giving $$c = \sqrt{2}$$.

The foci are at $$(0, \pm\sqrt{2})$$. The focus on the negative major axis is $$S = (0, -\sqrt{2})$$.

The tangent at a point $$(x_1, y_1)$$ on the ellipse is $$\frac{xx_1}{2} + \frac{yy_1}{4} = 1$$.

The tangents at P and Q both pass through $$R(\sqrt{2}, 2\sqrt{2} - 2)$$. So the chord of contact from $$R$$ to the ellipse is:

$$\frac{x \cdot \sqrt{2}}{2} + \frac{y(2\sqrt{2}-2)}{4} = 1$$

$$\frac{\sqrt{2}x}{2} + \frac{(2\sqrt{2}-2)y}{4} = 1$$

$$\frac{x}{\sqrt{2}} + \frac{(\sqrt{2}-1)y}{2} = 1$$

This is the equation of the chord PQ. Now we need to find P and Q (the points on the ellipse where this chord intersects).

From the chord equation: $$x = \sqrt{2}\left(1 - \frac{(\sqrt{2}-1)y}{2}\right) = \sqrt{2} - \frac{(\sqrt{2}-1)\sqrt{2}y}{2} = \sqrt{2} - \frac{(2 - \sqrt{2})y}{2}$$

Substituting into the ellipse equation $$\frac{x^2}{2} + \frac{y^2}{4} = 1$$:

$$\frac{\left[\sqrt{2} - \frac{(2-\sqrt{2})y}{2}\right]^2}{2} + \frac{y^2}{4} = 1$$

Let $$k = \frac{2-\sqrt{2}}{2}$$. Then $$x = \sqrt{2} - ky$$.

$$\frac{2 - 2\sqrt{2}ky + k^2y^2}{2} + \frac{y^2}{4} = 1$$

$$1 - \sqrt{2}ky + \frac{k^2y^2}{2} + \frac{y^2}{4} = 1$$

$$-\sqrt{2}ky + y^2\left(\frac{k^2}{2} + \frac{1}{4}\right) = 0$$

$$y\left[-\sqrt{2}k + y\left(\frac{k^2}{2} + \frac{1}{4}\right)\right] = 0$$

So $$y = 0$$ or $$y = \frac{\sqrt{2}k}{\frac{k^2}{2} + \frac{1}{4}}$$.

With $$k = \frac{2-\sqrt{2}}{2}$$: $$k^2 = \frac{(2-\sqrt{2})^2}{4} = \frac{6-4\sqrt{2}}{4}$$.

$$\frac{k^2}{2} + \frac{1}{4} = \frac{6-4\sqrt{2}}{8} + \frac{2}{8} = \frac{8-4\sqrt{2}}{8} = \frac{2-\sqrt{2}}{2}$$

$$y_2 = \frac{\sqrt{2} \cdot \frac{2-\sqrt{2}}{2}}{\frac{2-\sqrt{2}}{2}} = \sqrt{2}$$

So the two points have $$y_P = 0$$ and $$y_Q = \sqrt{2}$$.

For $$y = 0$$: $$x = \sqrt{2}$$. So $$P = (\sqrt{2}, 0)$$. Check: $$\frac{2}{2} + 0 = 1$$. ✓

For $$y = \sqrt{2}$$: $$x = \sqrt{2} - k\sqrt{2} = \sqrt{2}(1-k) = \sqrt{2}\left(1 - \frac{2-\sqrt{2}}{2}\right) = \sqrt{2} \cdot \frac{\sqrt{2}}{2} = 1$$. So $$Q = (1, \sqrt{2})$$. Check: $$\frac{1}{2} + \frac{2}{4} = 1$$. ✓

Now with $$S = (0, -\sqrt{2})$$:

$$SP^2 = (\sqrt{2}-0)^2 + (0-(-\sqrt{2}))^2 = 2 + 2 = 4$$

$$SQ^2 = (1-0)^2 + (\sqrt{2}-(-\sqrt{2}))^2 = 1 + (2\sqrt{2})^2 = 1 + 8 = 9$$

$$SP^2 + SQ^2 = 4 + 9 = 13$$

Hence, the correct answer is 13.

Given,

$$x^2+2y^2=2 \quad\cdots(1)$$ and $$x+y=1 \quad\cdots(2)$$ 

Let the points of intersection be $$P$$ and $$Q.$$

From (2),

$$y=1-x$$

Substitute into (1):

$$x^2+2(1-x)^2=2$$

$$x^2+2(1-2x+x^2)=2$$

$$3x^2-4x=0$$

$$x(3x-4)=0$$

Hence,

$$x=0\quad\text{or}\quad x=\frac43$$

Therefore,

$$P=(0,1)$$ and $$Q=\left(\frac43,-\frac13\right)$$

Now slopes of

$$OP$$ and $$OQ$$ are $$m_1=\infty$$ and $$m_2=\frac{-1/3}{4/3}=-\frac14$$

Hence,

$$OQ$$ makes an angle $$-\tan^{-1}\left(\frac14\right)$$ with the positive $$x$$-axis.

Since

$$OP$$ lies along the positive $$y$$-axis, it makes angle $$\frac\pi2$$ with the positive $$x$$-axis.

Therefore angle between $$OP$$ and $$OQ$$ is $$\frac\pi2-\left(-\tan^{-1}\left(\frac14\right)\right)$$

$$=\frac\pi2+\tan^{-1}\left(\frac14\right)$$

Hence, the angle subtended by $$PQ$$ at the origin is $$\boxed{\frac\pi2+\tan^{-1}\left(\frac14\right)}$$

We are given the ellipse $$E: \dfrac{x^2}{a^2} + \dfrac{y^2}{b^2} = 1$$ with $$a^2 > b^2$$, passing through $$\left(\sqrt{\dfrac{3}{2}},\, 1\right)$$ and having eccentricity $$e = \dfrac{1}{\sqrt{3}}$$.

Step 1: Find $$a^2$$ and $$b^2$$.

From the eccentricity relation:

$$e^2 = 1 - \frac{b^2}{a^2} \implies \frac{1}{3} = 1 - \frac{b^2}{a^2} \implies b^2 = \frac{2a^2}{3}$$

Since $$\left(\sqrt{\dfrac{3}{2}},\, 1\right)$$ lies on the ellipse:

$$\frac{3/2}{a^2} + \frac{1}{b^2} = 1$$

Substituting $$b^2 = \dfrac{2a^2}{3}$$:

$$\frac{3}{2a^2} + \frac{3}{2a^2} = 1 \implies \frac{3}{a^2} = 1 \implies a^2 = 3$$

Hence $$b^2 = 2$$, and the ellipse is $$\dfrac{x^2}{3} + \dfrac{y^2}{2} = 1$$.

Step 2: Identify the focus and circle.

$$c = \sqrt{a^2 - b^2} = \sqrt{3 - 2} = 1$$

The focus with positive $$x$$-coordinate is $$F(1, 0)$$. The circle centered at $$F$$ with radius $$\dfrac{2}{\sqrt{3}}$$ has equation:

$$(x - 1)^2 + y^2 = \frac{4}{3}$$

Step 3: Find the intersection points $$P$$ and $$Q$$.

From the ellipse: $$y^2 = 2 - \dfrac{2x^2}{3}$$

Substituting into the circle equation:

$$(x - 1)^2 + 2 - \frac{2x^2}{3} = \frac{4}{3}$$

$$x^2 - 2x + 1 + 2 - \frac{2x^2}{3} = \frac{4}{3}$$

$$\frac{x^2}{3} - 2x + 3 = \frac{4}{3}$$

$$x^2 - 6x + 9 = 4$$

$$x^2 - 6x + 5 = 0$$

$$(x - 1)(x - 5) = 0$$

So $$x = 1$$ or $$x = 5$$. For $$x = 5$$: $$y^2 = 2 - \dfrac{50}{3} < 0$$, which is invalid. Thus $$x = 1$$.

At $$x = 1$$: $$y^2 = 2 - \dfrac{2}{3} = \dfrac{4}{3}$$, giving $$y = \pm\dfrac{2}{\sqrt{3}}$$.

So $$P = \left(1,\, \dfrac{2}{\sqrt{3}}\right)$$ and $$Q = \left(1,\, -\dfrac{2}{\sqrt{3}}\right)$$.

Step 4: Calculate $$PQ^2$$.

$$PQ = \frac{2}{\sqrt{3}} + \frac{2}{\sqrt{3}} = \frac{4}{\sqrt{3}}$$

$$PQ^2 = \frac{16}{3}$$

The correct answer is Option C: $$\dfrac{16}{3}$$.

For ellipse $$E_1: \frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$$ with $$a > b$$, the major axis endpoints are $$(\pm a, 0)$$, the minor axis endpoints are $$(0, \pm b)$$, and the eccentricity is $$e$$ where $$b^2 = a^2(1 - e^2)$$ $$-(1)$$.

Ellipse $$E_2$$ touches the endpoints of the major axis of $$E_1$$, so $$E_2$$ passes through $$(\pm a, 0)$$. The foci of $$E_2$$ are the endpoints of the minor axis of $$E_1$$, i.e., $$(0, \pm b)$$.

Since the foci of $$E_2$$ lie on the $$y$$-axis, the major axis of $$E_2$$ is along the $$y$$-axis. Let $$E_2: \frac{x^2}{B^2} + \frac{y^2}{A^2} = 1$$ where $$A > B$$.

The foci of $$E_2$$ are at $$(0, \pm c_2)$$ where $$c_2^2 = A^2 - B^2$$. Since the foci are at $$(0, \pm b)$$, we get $$A^2 - B^2 = b^2$$ $$-(2)$$.

Since $$E_2$$ passes through $$(\pm a, 0)$$: $$\frac{a^2}{B^2} + 0 = 1$$, so $$B = a$$ $$-(3)$$.

From $$(2)$$ and $$(3)$$: $$A^2 = a^2 + b^2$$ $$-(4)$$.

The eccentricity of $$E_2$$ is $$e_2 = \frac{b}{A} = \frac{b}{\sqrt{a^2 + b^2}}$$.

Setting $$e_1 = e_2$$: $$\frac{\sqrt{a^2 - b^2}}{a} = \frac{b}{\sqrt{a^2 + b^2}}$$.

Squaring: $$\frac{a^2 - b^2}{a^2} = \frac{b^2}{a^2 + b^2}$$.

Cross-multiplying: $$(a^2 - b^2)(a^2 + b^2) = a^2 b^2$$, so $$a^4 - b^4 = a^2 b^2$$.

Dividing by $$a^4$$: let $$t = \frac{b^2}{a^2}$$, then $$1 - t^2 = t$$, so $$t^2 + t - 1 = 0$$.

Solving: $$t = \frac{-1 + \sqrt{5}}{2}$$ (taking the positive root).

Now $$e^2 = 1 - t = 1 - \frac{-1 + \sqrt{5}}{2} = \frac{3 - \sqrt{5}}{2}$$.

We can verify that $$e = \frac{-1+\sqrt{5}}{2}$$ satisfies $$e^2 = \frac{3 - \sqrt{5}}{2}$$: indeed $$\left(\frac{-1+\sqrt{5}}{2}\right)^2 = \frac{1 - 2\sqrt{5} + 5}{4} = \frac{6 - 2\sqrt{5}}{4} = \frac{3 - \sqrt{5}}{2}$$. This confirms $$e = \frac{-1+\sqrt{5}}{2}$$.

The answer is $$\frac{-1+\sqrt{5}}{2}$$, which is Option A.

The ellipse is $$\frac{x^2}{16} + \frac{y^2}{b^2} = 1$$, the circle is $$x^2 + y^2 = 4b$$ with $$b > 4$$, and the intersection points lie on $$y^2 = 3x^2$$.

Substituting $$y^2 = 3x^2$$ into the circle equation: $$x^2 + 3x^2 = 4b$$, so $$x^2 = b$$.

Substituting $$x^2 = b$$ and $$y^2 = 3b$$ into the ellipse equation: $$\frac{b}{16} + \frac{3b}{b^2} = 1$$, which gives $$\frac{b}{16} + \frac{3}{b} = 1$$.

Multiplying through by $$16b$$: $$b^2 + 48 = 16b$$, so $$b^2 - 16b + 48 = 0$$.

Using the quadratic formula: $$b = \frac{16 \pm \sqrt{256 - 192}}{2} = \frac{16 \pm 8}{2}$$, giving $$b = 12$$ or $$b = 4$$. Since $$b > 4$$, we have $$b = 12$$.

The ellipse is $$\frac{x^2}{27} + y^2 = 1$$ and the point of tangency is $$(3\sqrt{3}\cos\theta, \sin\theta)$$. The equation of the tangent at this point is $$\frac{x \cdot 3\sqrt{3}\cos\theta}{27} + \frac{y \cdot \sin\theta}{1} = 1$$, which simplifies to $$\frac{x\cos\theta}{3\sqrt{3}} + y\sin\theta = 1$$.

The x-intercept is found by setting $$y = 0$$: $$x = \frac{3\sqrt{3}}{\cos\theta}$$. The y-intercept is found by setting $$x = 0$$: $$y = \frac{1}{\sin\theta}$$. The sum of intercepts is $$S(\theta) = \frac{3\sqrt{3}}{\cos\theta} + \frac{1}{\sin\theta} = 3\sqrt{3}\sec\theta + \csc\theta$$.

To minimize, we differentiate and set equal to zero: $$S'(\theta) = 3\sqrt{3}\sec\theta\tan\theta - \csc\theta\cot\theta = 0$$. This gives $$3\sqrt{3}\frac{\sin\theta}{\cos^2\theta} = \frac{\cos\theta}{\sin^2\theta}$$, so $$3\sqrt{3}\sin^3\theta = \cos^3\theta$$, hence $$\tan^3\theta = \frac{1}{3\sqrt{3}} = \frac{1}{\sqrt{27}}$$, giving $$\tan\theta = \frac{1}{\sqrt{3}}$$, and therefore $$\theta = \frac{\pi}{6}$$.

We are given the straight line

$$12x\cos\theta \;+\; 5y\sin\theta \;=\; 60.$$

Our task is to decide which one of the four given curves has this line as a tangent (for some value of the parameter $$\theta$$). To see this clearly we first put the equation of the line in a form that can be compared with the standard tangent form of conic sections.

Dividing every term by $$60$$ we get

$$\frac{12x\cos\theta}{60} \;+\; \frac{5y\sin\theta}{60} \;=\; 1.$$

Reducing the fractions step by step,

$$\frac{12}{60} \;=\; \frac{1}{5}, \qquad \frac{5}{60} \;=\; \frac{1}{12},$$

so the equation becomes

$$\frac{x\cos\theta}{5} \;+\; \frac{y\sin\theta}{12} \;=\; 1.$$

Now we recall the standard result for an ellipse. For the ellipse whose equation is

$$\frac{x^{2}}{a^{2}} \;+\; \frac{y^{2}}{b^{2}} \;=\; 1,$$

the equation of a tangent at the point $$\bigl(a\cos\phi,\;b\sin\phi\bigr)$$ on the ellipse is

$$\frac{x\cos\phi}{a} \;+\; \frac{y\sin\phi}{b} \;=\; 1.$$

Comparing our rearranged line

$$\frac{x\cos\theta}{5} \;+\; \frac{y\sin\theta}{12} \;=\; 1$$

term by term with the general tangent form

$$\frac{x\cos\phi}{a} \;+\; \frac{y\sin\phi}{b} \;=\; 1,$$

we see an exact match when we identify

$$a \;=\; 5, \qquad b \;=\; 12.$$

Hence the curve whose tangents are described by the given family of lines is the ellipse

$$\frac{x^{2}}{5^{2}} \;+\; \frac{y^{2}}{12^{2}} \;=\; 1,$$

that is,

$$\frac{x^{2}}{25} \;+\; \frac{y^{2}}{144} \;=\; 1.$$

To place this ellipse in the exact form used in the options, we clear denominators by multiplying every term by the least common multiple $$25 \times 144 = 3600$$:

$$144x^{2} \;+\; 25y^{2} \;=\; 3600.$$

This matches Option B exactly.

Hence, the correct answer is Option B.

The parabola is $$y^2 = 4x - 20 = 4(x - 5)$$. This is a parabola with vertex at $$(5, 0)$$ and parameter $$a = 1$$, opening rightward.

To find the tangent at $$(6, 2)$$, we differentiate $$y^2 = 4(x-5)$$ implicitly: $$2y \frac{dy}{dx} = 4$$, so $$\frac{dy}{dx} = \frac{2}{y} = \frac{2}{2} = 1$$ at the point $$(6, 2)$$.

The tangent line at $$(6, 2)$$ with slope $$1$$ is: $$y - 2 = 1 \cdot (x - 6)$$, giving $$y = x - 4$$.

For this line to be tangent to the ellipse $$\frac{x^2}{2} + \frac{y^2}{b} = 1$$, we substitute $$y = x - 4$$ into the ellipse equation: $$\frac{x^2}{2} + \frac{(x-4)^2}{b} = 1$$.

Multiplying through by $$2b$$: $$bx^2 + 2(x-4)^2 = 2b$$.

Expanding: $$bx^2 + 2x^2 - 16x + 32 = 2b$$, which gives $$(b+2)x^2 - 16x + (32 - 2b) = 0$$.

For tangency, the discriminant must equal zero: $$(-16)^2 - 4(b+2)(32-2b) = 0$$.

$$256 - 4(32b - 2b^2 + 64 - 4b) = 0$$, so $$256 - 4(-2b^2 + 28b + 64) = 0$$.

$$256 + 8b^2 - 112b - 256 = 0$$, giving $$8b^2 - 112b = 0$$, so $$8b(b - 14) = 0$$.

Since $$b \neq 0$$, we get $$b = 14$$.

The answer is $$14$$, which is Option B.

We have two curves, the ellipse $$\dfrac{x^{2}}{9}+\dfrac{y^{2}}{1}=1$$ and the circle $$x^{2}+y^{2}=3$$. First we locate their points of intersection in the first quadrant by solving the two equations simultaneously.

From the ellipse we get $$y^{2}=1-\dfrac{x^{2}}{9}.$$ Substituting this in the circle gives

$$x^{2}+1-\dfrac{x^{2}}{9}=3.$$

Collecting the $$x^{2}$$ terms,

$$x^{2}-\dfrac{x^{2}}{9}=3-1 \;\;\Longrightarrow\;\; \left(1-\dfrac{1}{9}\right)x^{2}=2.$$

Since $$1-\dfrac{1}{9}=\dfrac{8}{9},$$ we get

$$\dfrac{8}{9}x^{2}=2 \;\;\Longrightarrow\;\; x^{2}=2\cdot\dfrac{9}{8}=\dfrac{18}{8}=\dfrac{9}{4}.$$

Because we want the first-quadrant point, $$x=\dfrac{3}{2}>0.$$ Now we use $$y^{2}=1-\dfrac{x^{2}}{9}$$ to find $$y$$:

$$y^{2}=1-\dfrac{9/4}{9}=1-\dfrac{1}{4}=\dfrac{3}{4}\;\;\Longrightarrow\;\;y=\dfrac{\sqrt{3}}{2}>0.$$

Thus the common point is $$P\!\left(\dfrac{3}{2},\dfrac{\sqrt{3}}{2}\right).$$

Next we write the tangent to each curve at $$P$$.

For the ellipse $$\dfrac{x^{2}}{a^{2}}+\dfrac{y^{2}}{b^{2}}=1,$$ the tangent at $$(x_{1},y_{1})$$ is given by the standard formula $$\dfrac{xx_{1}}{a^{2}}+\dfrac{yy_{1}}{b^{2}}=1.$$ Here $$a^{2}=9,\;b^{2}=1,\;x_{1}=\dfrac{3}{2},\;y_{1}=\dfrac{\sqrt{3}}{2},$$ so

$$\dfrac{x\!\left(\dfrac{3}{2}\right)}{9}+y\!\left(\dfrac{\sqrt{3}}{2}\right)=1.$$

Simplifying, $$\dfrac{3x}{18}+\dfrac{\sqrt{3}}{2}y=1 \;\;\Longrightarrow\;\; \dfrac{x}{6}+\dfrac{\sqrt{3}}{2}y=1.$$

Solving for $$y$$ in slope-intercept form,

$$\dfrac{\sqrt{3}}{2}y=1-\dfrac{x}{6} \;\;\Longrightarrow\;\; y=\dfrac{2}{\sqrt{3}}\!\left(1-\dfrac{x}{6}\right)=\dfrac{2}{\sqrt{3}}-\dfrac{x}{3\sqrt{3}}.$$

Hence the slope of the ellipse tangent is

$$m_{e}=-\dfrac{1}{3\sqrt{3}}.$$

For a circle $$x^{2}+y^{2}=r^{2}$$ centred at the origin, the tangent at $$(x_{1},y_{1})$$ is $$xx_{1}+yy_{1}=r^{2}.$$ Using $$x_{1}=\dfrac{3}{2},\;y_{1}=\dfrac{\sqrt{3}}{2},\;r^{2}=3,$$ we obtain

$$x\!\left(\dfrac{3}{2}\right)+y\!\left(\dfrac{\sqrt{3}}{2}\right)=3.$$

Multiplying by $$2,$$ $$3x+\sqrt{3}\,y=6.$$ Solving for $$y,$$

$$\sqrt{3}\,y=6-3x \;\;\Longrightarrow\;\; y=\dfrac{6-3x}{\sqrt{3}}=2\sqrt{3}-x\sqrt{3}.$$

Thus the slope of the circle tangent is

$$m_{c}=-\sqrt{3}.$$

Now we need the acute angle $$\theta$$ between the two tangents. For lines with slopes $$m_{1}$$ and $$m_{2}$$ we use the formula

$$\tan\theta=\left|\dfrac{m_{2}-m_{1}}{1+m_{1}m_{2}}\right|.$$

Taking $$m_{1}=m_{e}=-\dfrac{1}{3\sqrt{3}}$$ and $$m_{2}=m_{c}=-\sqrt{3},$$

$$m_{2}-m_{1}=-\sqrt{3}-\left(-\dfrac{1}{3\sqrt{3}}\right) =-\sqrt{3}+\dfrac{1}{3\sqrt{3}} =\dfrac{-8}{3\sqrt{3}},$$

and

$$1+m_{1}m_{2}=1+\left(-\dfrac{1}{3\sqrt{3}}\right)\!\left(-\sqrt{3}\right)=1+\dfrac{1}{3}=\dfrac{4}{3}.$$

Therefore

$$\tan\theta=\left|\dfrac{-8/(3\sqrt{3})}{4/3}\right| =\dfrac{8}{3\sqrt{3}}\cdot\dfrac{3}{4} =\dfrac{2}{\sqrt{3}}.$$

Hence, the correct answer is Option C.

First we note that the light is incident from the point $$(2,1)$$, strikes a point $$P$$ on the $$y$$-axis and afterwards travels through the point $$(5,3)$$. A vertical mirror is modelled by the line $$x=0$$ (the $$y$$-axis). Whenever a ray reflects from a straight mirror, the “law of reflection” tells us that the actual broken path is equivalent to a straight line that joins the image of the source with the final point. Concretely, if we reflect the source $$A(2,1)$$ in the line $$x=0$$, its mirror image becomes $$A'(-2,1)$$. Therefore the straight line $$A'B$$, where $$B(5,3)$$ is the final point, meets the $$y$$-axis exactly at the required point of incidence $$P$$.

The slope of the line joining $$A'(-2,1)$$ and $$B(5,3)$$ is

$$m=\frac{3-1}{5-(-2)}=\frac{2}{7}.$$

Using the two-point form, the equation of $$A'B$$ is

$$y-1=\frac{2}{7}\,(x+2).$$

To find $$P$$ we put $$x=0$$ (because $$P$$ lies on the $$y$$-axis):

$$y-1=\frac{2}{7}\,(0+2)=\frac{4}{7}\;\Longrightarrow\;y=1+\frac{4}{7}=\frac{11}{7}.$$

Hence $$P\left(0,\frac{11}{7}\right)$$. After reflection the ray simply follows the same straight line through $$P$$ and $$B$$, so this reflected ray is the line

$$y-\frac{11}{7}=\frac{2}{7}\,(x-0).$$

Multiplying by $$7$$ gives $$7y-11=2x$$, or, in the standard form,

$$2x-7y+11=0.$$

This line is given in the statement to be a directrix of an ellipse whose eccentricity is $$e=\dfrac13$$.

For any ellipse the two directrices are parallel; the major axis is perpendicular to them. Every focus lies on this axis. The distance from a focus to its corresponding directrix is related to the semi-major axis length $$a$$ by the well-known formula

$$\text{distance (focus, directrix)} = a\!\left(\frac1e-e\right).$$

We are told that the nearer focus is at a perpendicular distance $$\dfrac{8}{\sqrt{53}}$$ from the directrix $$2x-7y+11=0$$. Therefore, writing the above relation explicitly, we have

$$a\!\left(\frac1e-e\right)=\frac{8}{\sqrt{53}}.$$

Substituting $$e=\dfrac13$$ gives

$$a\!\left(3-\frac13\right)=a\!\left(\frac{9-1}{3}\right)=a\!\left(\frac{8}{3}\right)=\frac{8}{\sqrt{53}},$$

$$\Longrightarrow\;a=\frac{8}{\sqrt{53}}\cdot\frac{3}{8}=\frac{3}{\sqrt{53}}.$$

For an ellipse the distance between its two directrices is $$\dfrac{2a}{e}$$ (because each directrix is at the distance $$\dfrac{a}{e}$$ from the centre on opposite sides). Hence, with $$a=\dfrac{3}{\sqrt{53}}$$ and $$e=\dfrac13$$, the separation of the directrices is

$$\frac{2a}{e}=2a\!\left(\frac{1}{e}\right)=2a\cdot3=6a=6\left(\frac{3}{\sqrt{53}}\right)=\frac{18}{\sqrt{53}}.$$

Now let us write the equation of a general line that is parallel to the given directrix. Any line parallel to

$$2x-7y+11=0$$

has the form

$$2x-7y+k=0,$$

where $$k$$ is a constant. The perpendicular distance between two such parallel lines

$$2x-7y+11=0\quad\text{and}\quad 2x-7y+k=0$$

is

$$\frac{|k-11|}{\sqrt{2^{2}+(-7)^{2}}}=\frac{|k-11|}{\sqrt{4+49}}=\frac{|k-11|}{\sqrt{53}}.$$

Setting this equal to the required separation $$\dfrac{18}{\sqrt{53}}$$, we obtain

$$\frac{|k-11|}{\sqrt{53}}=\frac{18}{\sqrt{53}}

\;\Longrightarrow\;

|k-11|=18.$$

So

$$k-11=18\quad\text{or}\quad k-11=-18,$$

$$k=29\quad\text{or}\quad k=-7.$$

Consequently the second directrix can be either

$$2x-7y+29=0\quad\text{or}\quad 2x-7y-7=0.$$

These two equations appear exactly in option (C).

Hence, the correct answer is Option C.

Given curves

$$\frac{x^2}{a}+\frac{y^2}{b}=1 \quad\cdots(1)$$ and $$\frac{x^2}{c}+\frac{y^2}{d}=1 \quad\cdots(2)$$ intersect orthogonally.

We need to find the correct relation among $$a,b,c,d.$$

Differentiate (1):

$$\frac{2x}{a}+\frac{2y}{b}\frac{dy}{dx}=0$$

$$\frac{dy}{dx}=-\frac{bx}{ay}$$

Hence slope of tangent to (1) is $$m_1=-\frac{bx}{ay}$$

Now differentiate (2): $$\frac{2x}{c}+\frac{2y}{d}\frac{dy}{dx}=0$$

$$\frac{dy}{dx} =-\frac{dx}{cy}$$

Hence slope of tangent to (2) is $$m_2=-\frac{dx}{cy}$$

Since the curves intersect at $$90^\circ,$$ their tangents are perpendicular.

Therefore,

$$m_1m_2=-1$$

Substituting,

$$\left(-\frac{bx}{ay}\right) \left(-\frac{dx}{cy}\right)=-1$$

$$\frac{bdx^2}{acy^2}=-1 \quad\cdots(3)$$

Now from equations (1) and (2),

$$\frac{x^2}{a}+\frac{y^2}{b}=1$$

$$\frac{x^2}{c}+\frac{y^2}{d}=1$$

Subtracting,

$$x^2\left(\frac1a-\frac1c\right)+y^2\left(\frac1b-\frac1d\right)=0$$

$$x^2\frac{c-a}{ac} +y^2\frac{d-b}{bd}=0$$

$$bd(c-a)x^2 +ac(d-b)y^2=0$$

$$bd(a-c)x^2 =ac(d-b)y^2 \quad\cdots(4)$$

Using (3),

$$\frac{x^2}{y^2} =\frac{-ac}{bd}$$

Substitute into (4):

$$bd(a-c)\left(\frac{-ac}{bd}\right) =ac(d-b)$$

$$-(a-c)=d-b$$

$$a-c=b-d$$

Hence,

$$a-b=c-d$$

Therefore, the correct option is

$$\boxed{a-b=c-d}$$

We start with the ellipse $$\dfrac{x^{2}}{8}+\dfrac{y^{2}}{4}=1$$ whose semi-major axis is along the x-axis because $$a^{2}=8\gt b^{2}=4$$. So we have $$a=\sqrt 8=2\sqrt2,\;b=\sqrt4=2.$$

The given condition is that the tangent at a point $$P(x_{1},y_{1})$$ on the ellipse is perpendicular to the straight line $$x+2y=0.$$

First, write the slope of the given straight line. Solving $$x+2y=0$$ for $$y$$ gives $$y=-\dfrac{x}{2},$$ so its slope is $$m_{1}=-\dfrac12.$$

If two lines are perpendicular, then the product of their slopes equals $$-1.$$ Hence, if the slope of the tangent at $$P$$ is $$m,$$ we must have

$$m\cdot\Bigl(-\dfrac12\Bigr)=-1\;\Longrightarrow\;m=2.$$

Now, we need the slope of the tangent to the ellipse. Using implicit differentiation on $$\dfrac{x^{2}}{8}+\dfrac{y^{2}}{4}=1,$$ we have

$$$\dfrac{2x}{8}+\dfrac{2y}{4}\dfrac{dy}{dx}=0 \;\Longrightarrow\;\dfrac{x}{4}+ \dfrac{y}{2}\dfrac{dy}{dx}=0 \;\Longrightarrow\;\dfrac{dy}{dx}=-\dfrac{x}{2y}.$$$

Therefore the slope at $$P(x_{1},y_{1})$$ is $$m=-\dfrac{x_{1}}{2y_{1}}.$$ Equating this slope to the required value $$2,$$ we get

$$-\dfrac{x_{1}}{2y_{1}}=2 \;\Longrightarrow\;x_{1}=-4y_{1}.$$

Because $$P$$ lies on the ellipse, its coordinates must also satisfy $$\dfrac{x_{1}^{2}}{8}+\dfrac{y_{1}^{2}}{4}=1.$$ Substituting $$x_{1}=-4y_{1}$$ into this equation, we obtain

$$$\dfrac{(-4y_{1})^{2}}{8}+\dfrac{y_{1}^{2}}{4}=1 \;\Longrightarrow\;\dfrac{16y_{1}^{2}}{8}+\dfrac{y_{1}^{2}}{4}=1 \;\Longrightarrow\;2y_{1}^{2}+\dfrac{y_{1}^{2}}{4}=1 \;\Longrightarrow\;\dfrac{8y_{1}^{2}+y_{1}^{2}}{4}=1 \;\Longrightarrow\;\dfrac{9y_{1}^{2}}{4}=1 \;\Longrightarrow\;y_{1}^{2}=\dfrac{4}{9} \;\Longrightarrow\;y_{1}=\dfrac{2}{3}\quad(\text{positive because }P\text{ is in the second quadrant}).$$$

Using $$x_{1}=-4y_{1},$$ we now get

$$x_{1}=-4\left(\dfrac{2}{3}\right)=-\dfrac{8}{3}.$$

Thus the required point is $$P\!\left(-\dfrac83,\dfrac23\right).$$ Its x-coordinate is negative and y-coordinate positive, confirming that $$P$$ is indeed in the second quadrant.

Next we determine the foci of the ellipse. For an ellipse $$\dfrac{x^{2}}{a^{2}}+\dfrac{y^{2}}{b^{2}}=1$$ with $$a\gt b,$$ the distance of each focus from the centre is $$c=\sqrt{a^{2}-b^{2}}.$$ Here

$$c=\sqrt{8-4}=2.$$

Hence the foci are $$S(2,0)$$ and $$S'(-2,0).$$ The eccentricity $$e$$ is defined as $$e=\dfrac{c}{a},$$ so

$$e=\dfrac{2}{2\sqrt2}=\dfrac1{\sqrt2},\qquad e^{2}=\dfrac12.$$

We must now find the area $$A$$ of the triangle $$\triangle SPS'$$ with vertices

$$$S(2,0),\;P\!\left(-\dfrac83,\dfrac23\right),\;S'(-2,0).$$$

The simplest approach is the coordinate (shoelace) formula for the area of a triangle:

$$$A=\dfrac12\left|x_{1}(y_{2}-y_{3})+x_{2}(y_{3}-y_{1})+x_{3}(y_{1}-y_{2})\right|.$$$

Label $$$S(x_{1},y_{1})=(2,0),\;P(x_{2},y_{2})=\left(-\dfrac83,\dfrac23\right),\;S'(x_{3},y_{3})=(-2,0).$$$ Substituting, we get

$$$ \begin{aligned} A&=\dfrac12\Biggl|\,2\!\left(\dfrac23-0\right) +\left(-\dfrac83\right)(0-0) +(-2)\!\left(0-\dfrac23\right)\Biggr|\\[2mm] &=\dfrac12\Biggl|\;2\cdot\dfrac23+0+(-2)\!\left(-\dfrac23\right)\Biggr|\\[2mm] &=\dfrac12\Biggl|\;\dfrac43+\dfrac43\Biggr|\\[2mm] &=\dfrac12\cdot\dfrac83=\dfrac43. \end{aligned} $$$

So, $$A=\dfrac43.$$

Finally we evaluate $$(5-e^{2})\cdot A.$$ We have already found $$e^{2}=\dfrac12,$$ therefore

$$$ (5-e^{2})\cdot A =\left(5-\dfrac12\right)\cdot\dfrac43 =\dfrac{9}{2}\cdot\dfrac43 =\dfrac{9\cdot4}{2\cdot3} =\dfrac{36}{6} =6. $$$

Hence, the correct answer is Option B.

We begin with the ellipse

$$x^{2}+4y^{2}=4.$$

It can be rewritten as $$\dfrac{x^{2}}{4}+\dfrac{y^{2}}{1}=1,$$ so we have

$$a^{2}=4,\qquad b^{2}=1,\qquad a=2,\qquad b=1.$$

Because $$a\gt b,$$ the major axis is the $$x$$-axis and its extremities are the end points

$$A_{1}(2,0)\quad\text{and}\quad A_{2}(-2,0).$$

For an ellipse $$\dfrac{x^{2}}{a^{2}}+\dfrac{y^{2}}{b^{2}}=1,$$ the tangent at a point $$(x_{1},y_{1})$$ is

$$\dfrac{xx_{1}}{a^{2}}+\dfrac{yy_{1}}{b^{2}}=1.$$

At $$(2,0)$$ this gives $$\dfrac{x\cdot2}{4}=1\;\Longrightarrow\;x=2,$$ and at $$(-2,0)$$ it gives $$\dfrac{x(-2)}{4}=1\;\Longrightarrow\;x=-2.$$

Thus the tangents at the extremities of the major axis are the two vertical lines

$$x=2\qquad\text{and}\qquad x=-2.$$

Now let us draw an arbitrary tangent to the ellipse that has slope $$m$$. For the ellipse in slope form the tangent is

$$y=mx\pm\sqrt{a^{2}m^{2}+b^{2}},$$

and with $$a^{2}=4,\;b^{2}=1$$ this becomes

$$y=mx\pm\sqrt{4m^{2}+1}.$$

Denote the quantity $$D=\sqrt{4m^{2}+1},\qquad D\gt 0.$$

Choosing the ‘$$+$$’ sign (the ‘$$-$$’ sign gives the same straight line shifted in $$y$$ by an overall minus and therefore the same pair of points $$B,C$$), the tangent is

$$y=mx+D.$$

We next find its intersections with the two fixed vertical lines.

Intersection with $$x=2$$ :

Substitute $$x=2$$ in $$y=mx+D$$ to obtain

$$y_{B}=m\cdot2+D=2m+D.$$

Hence $$B(2,\;2m+D).$$

Intersection with $$x=-2$$ :

Substitute $$x=-2$$ to get

$$y_{C}=m(-2)+D=-2m+D.$$

Hence $$C(-2,\;-2m+D).$$

Thus the endpoints of segment $$BC$$ are

$$B(2,\;2m+D),\qquad C(-2,\;-2m+D).$$

We must study the circle having $$BC$$ as its diameter. A very useful fact is the following:

For a segment with endpoints $$(x_{1},y_{1})$$ and $$(x_{2},y_{2})$$, a point $$(x,y)$$ lies on the circle with that segment as diameter if and only if

$$ (x-x_{1})(x-x_{2})+(y-y_{1})(y-y_{2})=0. $$

This is simply the algebraic translation of “$$\angle BPC$$ is a right angle” (the dot‐product of the vectors $$\overrightarrow{PB}$$ and $$\overrightarrow{PC}$$ must be zero).

Applying the criterion with $$B(2,2m+D)$$ and $$C(-2,-2m+D)$$, we get that a point $$P(x,y)$$ will be on the required circle iff

$$$ \bigl(x-2\bigr)\bigl(x+2\bigr)+\bigl(y-(2m+D)\bigr)\bigl(y-(-2m+D)\bigr)=0. $$$

The first bracket simplifies immediately:

$$ (x-2)(x+2)=x^{2}-4. $$

For the second product we write the two subtractions explicitly and use the identity $$(A-B)(A+B)=A^{2}-B^{2}$$:

$$$ \begin{aligned} (y-2m-D)(y+2m-D) &=(y-D-2m)(y-D+2m)\\ &=(y-D)^{2}-(2m)^{2}\\ &=(y-D)^{2}-4m^{2}. \end{aligned} $$$

Putting both parts together, the condition for $$P(x,y)$$ becomes

$$ x^{2}-4+\bigl(y-D\bigr)^{2}-4m^{2}=0. \quad -(★)$$

We now check each of the four option points one by one. Remember that $$D=\sqrt{4m^{2}+1}.$$

Option A $$\bigl(\sqrt{3},0\bigr)$$ :

Insert $$x=\sqrt{3},\;y=0$$ into (★).

First term: $$x^{2}-4=(\sqrt{3})^{2}-4=3-4=-1.$$

Second term: $$\bigl(y-D\bigr)^{2}=(0-D)^{2}=D^{2}=4m^{2}+1.$$

Hence the left side of (★) is

$$$ -1+(4m^{2}+1)-4m^{2}=0. $$$

It is identically zero for every real value of the slope $$m$$. Therefore the point $$(\sqrt{3},0)$$ always lies on the circle whose diameter is $$BC$$.

Option B $$\bigl(\sqrt{2},0\bigr)$$ :

Put $$x=\sqrt{2},\;y=0$$ in (★).

$$x^{2}-4=2-4=-2$$.

Second term remains $$D^{2}=4m^{2}+1$$.

Total $$-2+(4m^{2}+1)-4m^{2}=-1\neq0,$$ so $$(\sqrt{2},0)$$ is not on the required circle.

Option C $$(1,1)$$ :

$$x^{2}-4=1-4=-3.$$

$$(y-D)^{2}=(1-D)^{2}=1-2D+D^{2}=1-2D+4m^{2}+1=2-2D+4m^{2}.$$

Total $$-3+\bigl(2-2D+4m^{2}\bigr)-4m^{2}=-1-2D\neq0.$$

So $$(1,1)$$ is not on the circle.

Option D $$(-1,1)$$ :

$$x^{2}-4=1-4=-3.$$

$$(y-D)^{2}=(1-D)^{2}$$ is the same as above, giving $$2-2D+4m^{2}.$$

Total $$-3+\bigl(2-2D+4m^{2}\bigr)-4m^{2}=-1-2D\neq0.$$

Therefore $$(-1,1)$$ is also excluded.

Only the first option satisfies the circle condition for every tangent, so the circle with $$BC$$ as diameter always passes through the point $$(\sqrt{3},0)$$.

Hence, the correct answer is Option A.

We need to find which curve has the line $$x + \sqrt{3}y = 2\sqrt{3}$$ as a tangent at the point $$\left(\frac{3\sqrt{3}}{2}, \frac{1}{2}\right)$$.

Consider the ellipse $$x^2 + 9y^2 = 9$$. First, we verify that the point lies on this curve: $$\left(\frac{3\sqrt{3}}{2}\right)^2 + 9\left(\frac{1}{2}\right)^2 = \frac{27}{4} + \frac{9}{4} = \frac{36}{4} = 9$$. The point is indeed on the ellipse.

The equation of the tangent to the ellipse $$\frac{x^2}{9} + \frac{y^2}{1} = 1$$ at the point $$(x_1, y_1)$$ is $$\frac{xx_1}{9} + yy_1 = 1$$.

Substituting $$(x_1, y_1) = \left(\frac{3\sqrt{3}}{2}, \frac{1}{2}\right)$$, the tangent is $$\frac{x \cdot \frac{3\sqrt{3}}{2}}{9} + y \cdot \frac{1}{2} = 1$$, which simplifies to $$\frac{\sqrt{3}x}{6} + \frac{y}{2} = 1$$.

Multiplying through by 6 gives $$\sqrt{3}x + 3y = 6$$. Dividing by $$\sqrt{3}$$, we get $$x + \sqrt{3}y = \frac{6}{\sqrt{3}} = 2\sqrt{3}$$.

This matches the given tangent line $$x + \sqrt{3}y = 2\sqrt{3}$$.

Therefore, the curve is $$x^2 + 9y^2 = 9$$.

1. Parametric Form of the Tangent

The given ellipse is:

$$\frac{x^2}{b^2} + \frac{y^2}{(2a)^2} = 1$$

Any point on this ellipse can be represented in parametric form as:

$$(x_1, y_1) = (b \cos\theta, 2a \sin\theta)$$

The equation of the tangent at this point is given by:

$$\frac{x \cos\theta}{b} + \frac{y \sin\theta}{2a} = 1$$

2. Intercepts on Coordinate Axes

To find where the tangent cuts the axes:

X-intercept (put $$y = 0$$): $$x = \frac{b}{\cos\theta}$$

Y-intercept (put $$x = 0$$): $$y = \frac{2a}{\sin\theta}$$

3. Area of the Triangle

The area $$\Delta$$ of the right-angled triangle formed with the axes is:

$$\Delta = \frac{1}{2} \times \vert{}X\text{-intercept}\vert{} \times \vert{}Y\text{-intercept}\vert{}$$

$$\Delta = \frac{1}{2} \times \left\vert{}\frac{b}{\cos\theta}\right\vert{} \times \left\vert{}\frac{2a}{\sin\theta}\right\vert{}$$

$$\Delta = \frac{ab}{\vert{}\sin\theta \cos\theta\vert{}} = \frac{2ab}{\vert{}2\sin\theta \cos\theta\vert{}} = \frac{2ab}{\vert{}\sin 2\theta\vert{}}$$

4. Minimum Area Condition

For the area to be minimum, the denominator $$\vert{}\sin 2\theta\vert{}$$ must be maximum:

Maximum value of $$\vert{}\sin 2\theta\vert{} = 1$$

$$\Delta_{\min} = \frac{2ab}{1} = 2ab$$

Comparing this with the given minimum area $$kab$$:

$$kab = 2ab \implies k = 2$$

Answer:

The value of $$k$$ is $$2$$.

We have an ellipse whose centre is $$(3,-4)$$ and whose axes are parallel to the coordinate axes, so its equation can be written as $$\frac{(x-3)^2}{a^2}+\frac{(y+4)^2}{b^2}=1.$$ Because the given focus $$(4,-4)$$ and the given vertex $$(5,-4)$$ share the same ordinate as the centre, the major axis is clearly horizontal.

The distance from the centre to a vertex equals the semi-major axis length, so $$a = 5-3 = 2 \quad\Longrightarrow\quad a^2 = 4.$$ The distance from the centre to a focus equals the linear eccentricity, so $$c = 4-3 = 1 \quad\Longrightarrow\quad c^2 = 1.$$

For every ellipse with horizontal major axis, the relation $$c^2 = a^2 - b^2$$ holds. Substituting $$a^2 = 4$$ and $$c^2 = 1$$ we obtain $$b^2 = a^2 - c^2 = 4 - 1 = 3.$$ Hence the explicit equation of the ellipse is $$\frac{(x-3)^2}{4}+\frac{(y+4)^2}{3}=1.$$

The line $$mx - y = 4, \; m\gt 0$$ can be rewritten as $$y = mx - 4.$$ Adding 4 to both sides gives $$y + 4 = mx.$$

To check whether this line is a tangent, we substitute $$y = mx - 4$$ (equivalently $$y + 4 = mx$$) into the ellipse:

$$\frac{(x-3)^2}{4} + \frac{(mx)^2}{3} = 1.$$

Expanding $$(x-3)^2$$ yields $$x^2 - 6x + 9,$$ so $$\frac{x^2 - 6x + 9}{4} + \frac{m^2x^2}{3} = 1.$$

Multiplying every term by the L.C.M. $$12$$ clears denominators: $$3(x^2 - 6x + 9) + 4m^2x^2 = 12.$$

Simplifying term by term, $$3x^2 - 18x + 27 + 4m^2x^2 = 12.$$ Collecting like terms, $$(3 + 4m^2)x^2 - 18x + 15 = 0.$$

This quadratic in $$x$$ represents the intersection points of the line with the ellipse. For the line to be a tangent, the quadratic must have exactly one real root, so its discriminant must vanish. Using the quadratic-equation discriminant formula $$\Delta = b^2 - 4ac,$$ here $$a = 3 + 4m^2,\quad b = -18,\quad c = 15.$$

Setting the discriminant to zero: $$(-18)^2 - 4(3 + 4m^2)(15) = 0.$$ Calculating step by step, $$324 - 60(3 + 4m^2) = 0,$$ $$324 - 180 - 240m^2 = 0,$$ $$144 - 240m^2 = 0.$$

Solving for $$m^2$$: $$240m^2 = 144,$$ $$m^2 = \frac{144}{240} = \frac{3}{5}.$$

The problem asks for the value of $$5m^2,$$ so $$5m^2 = 5\left(\frac{3}{5}\right) = 3.$$

So, the answer is $$3$$.

The tangent to ellipse $$x^2 + 4y^2 = 5$$ at $$P(1,1)$$ is $$x \cdot 1 + 4y \cdot 1 = 5$$, i.e., $$x + 4y = 5$$, giving $$y = \frac{5-x}{4}$$.

The upper half of the ellipse gives $$y = \frac{1}{2}\sqrt{5 - x^2}$$. The region is bounded between $$x = 1$$ and $$x = \sqrt{5}$$, with the tangent line above the ellipse in this interval (both meet at $$x=1$$ and the ellipse hits $$y=0$$ at $$x=\sqrt{5}$$ while the tangent is still positive there).

$$\text{Area} = \int_1^{\sqrt{5}} \left[\frac{5-x}{4} - \frac{1}{2}\sqrt{5-x^2}\right]dx$$

For the first integral: $$\int_1^{\sqrt{5}}\frac{5-x}{4}\,dx = \frac{1}{4}\left[5x - \frac{x^2}{2}\right]_1^{\sqrt{5}} = \frac{1}{4}\left[\left(5\sqrt{5} - \frac{5}{2}\right) - \left(5 - \frac{1}{2}\right)\right] = \frac{5\sqrt{5} - 7}{4}$$

For the second integral, using $$\int \sqrt{a^2-x^2}\,dx = \frac{x}{2}\sqrt{a^2-x^2} + \frac{a^2}{2}\arcsin\frac{x}{a} + C$$ with $$a^2=5$$:

$$\int_1^{\sqrt{5}}\frac{1}{2}\sqrt{5-x^2}\,dx = \frac{1}{2}\left[\frac{x}{2}\sqrt{5-x^2}+\frac{5}{2}\arcsin\frac{x}{\sqrt{5}}\right]_1^{\sqrt{5}} = \frac{1}{2}\left[\frac{5\pi}{4} - 1 - \frac{5}{2}\arcsin\frac{1}{\sqrt{5}}\right]$$

Using $$\arcsin\frac{1}{\sqrt{5}} = \frac{\pi}{2} - \cos^{-1}\frac{1}{\sqrt{5}}$$, the second integral becomes $$\frac{5\pi}{8} - \frac{1}{2} - \frac{5}{4}\left(\frac{\pi}{2} - \cos^{-1}\frac{1}{\sqrt{5}}\right) = -\frac{1}{2} + \frac{5}{4}\cos^{-1}\frac{1}{\sqrt{5}}$$.

$$\text{Area} = \frac{5\sqrt{5}-7}{4} - \left(-\frac{1}{2} + \frac{5}{4}\cos^{-1}\frac{1}{\sqrt{5}}\right) = \frac{5}{4}\sqrt{5} - \frac{7}{4} + \frac{2}{4} - \frac{5}{4}\cos^{-1}\frac{1}{\sqrt{5}}$$

$$= \frac{5}{4}\sqrt{5} - \frac{5}{4} - \frac{5}{4}\cos^{-1}\!\left(\frac{1}{\sqrt{5}}\right)$$

Matching with $$\alpha\sqrt{5} + \beta + \gamma\cos^{-1}\!\left(\frac{1}{\sqrt{5}}\right)$$, we get $$\alpha = \frac{5}{4}$$, $$\beta = -\frac{5}{4}$$, $$\gamma = -\frac{5}{4}$$.

$$|\alpha + \beta + \gamma| = \left|\frac{5}{4} - \frac{5}{4} - \frac{5}{4}\right| = \frac{5}{4} = 1.25$$

We are given that point $$P(x,y)$$ lies on the conic $$9x^2 + 16y^2 = 144$$.

First we rewrite the conic in standard ellipse form. Dividing every term by $$144$$, we obtain

$$\dfrac{9x^2}{144} + \dfrac{16y^2}{144} = 1.$$

Simplifying the fractions,

$$\dfrac{x^2}{16} + \dfrac{y^2}{9} = 1.$$

We recognise $$\dfrac{x^2}{a^2} + \dfrac{y^2}{b^2} = 1$$ as the standard equation of an ellipse centred at the origin with semi-major axis $$a$$ and semi-minor axis $$b$$. Comparing, we have

$$a^2 = 16 \quad\Rightarrow\quad a = 4, \qquad b^2 = 9 \quad\Rightarrow\quad b = 3.$$

For any ellipse, the distance from the centre to each focus (denoted $$c$$) satisfies the relation

$$c^2 = a^2 - b^2.$$

Substituting our values $$a^2 = 16$$ and $$b^2 = 9$$, we get

$$c^2 = 16 - 9 = 7 \;\;\Longrightarrow\;\; c = \sqrt{7}.$$

Hence the foci are located at $$(c,0)$$ and $$(-c,0),$$ namely $$(\sqrt{7},0)$$ and $$(-\sqrt{7},0).$$ These are exactly the points $$A$$ and $$B$$ given in the question.

Now we recall the fundamental property of an ellipse:

The sum of the distances from any point on an ellipse to its two foci is constant and equals $$2a$$.

Here, $$a = 4,$$ so

$$PA + PB = 2a = 2 \times 4 = 8.$$

Therefore the value of $$PA + PB$$ is a constant $$8$$ for every point $$P$$ on the given ellipse.

Hence, the correct answer is Option B.

First, we note that for every conic of the form $$\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1$$ (ellipse with the major axis along the $$x$$-axis) the eccentricity formula is $$e=\sqrt{1-\frac{b^{2}}{a^{2}}}$$.

The given ellipse is $$\frac{x^{2}}{18}+\frac{y^{2}}{4}=1$$, so we identify $$a^{2}=18$$ and $$b^{2}=4$$ with $$a>b$$.

Applying the ellipse eccentricity formula, we write

$$e_{1}=\sqrt{1-\frac{b^{2}}{a^{2}}}=\sqrt{1-\frac{4}{18}}.$$

Simplifying the fraction inside the square root,

$$\frac{4}{18}=\frac{2}{9},$$ so

$$e_{1}=\sqrt{1-\frac{2}{9}}=\sqrt{\frac{9}{9}-\frac{2}{9}}=\sqrt{\frac{7}{9}}.$$

Taking the square root of a fraction, we get

$$e_{1}=\frac{\sqrt7}{3}.$$

Next we consider the hyperbola $$\frac{x^{2}}{9}-\frac{y^{2}}{4}=1$$. The standard form $$\frac{x^{2}}{a^{2}}-\frac{y^{2}}{b^{2}}=1$$ (transverse axis along $$x$$) has eccentricity formula $$e=\sqrt{1+\frac{b^{2}}{a^{2}}}$$. Here $$a^{2}=9$$ and $$b^{2}=4$$.

Thus

$$e_{2}=\sqrt{1+\frac{b^{2}}{a^{2}}}=\sqrt{1+\frac{4}{9}}.$$

We simplify inside the root:

$$1+\frac{4}{9}=\frac{9}{9}+\frac{4}{9}=\frac{13}{9},$$ so

$$e_{2}=\sqrt{\frac{13}{9}}=\frac{\sqrt{13}}{3}.$$

Because the ordered pair $$(e_{1},e_{2})$$ lies on the ellipse $$15x^{2}+3y^{2}=k$$, we substitute $$x=e_{1}$$ and $$y=e_{2}$$ into that equation.

Hence

$$15(e_{1})^{2}+3(e_{2})^{2}=k.$$

We already have

$$e_{1}^{2}=\left(\frac{\sqrt7}{3}\right)^{2}=\frac{7}{9},\qquad e_{2}^{2}=\left(\frac{\sqrt{13}}{3}\right)^{2}=\frac{13}{9}.$$

Substituting these squared values, we obtain

$$k=15\left(\frac{7}{9}\right)+3\left(\frac{13}{9}\right).$$

Multiplying numerators and denominators,

$$15\left(\frac{7}{9}\right)=\frac{105}{9},\qquad 3\left(\frac{13}{9}\right)=\frac{39}{9}.$$

Adding the two fractions,

$$k=\frac{105}{9}+\frac{39}{9}=\frac{144}{9}.$$

Finally, dividing numerator by denominator,

$$\frac{144}{9}=16.$$

Thus $$k=16$$.

Hence, the correct answer is Option A.

For an ellipse written in the standard form $$\dfrac{x^{2}}{a^{2}}+\dfrac{y^{2}}{b^{2}}=1$$ we recall the basic facts first.

We have the two foci situated at $$\bigl(\pm c,0\bigr)$$ where $$c^2=a^2-b^2$$, so the distance between the foci is $$2c$$. The eccentricity is defined by $$e=\dfrac{c}{a}$$. The two corresponding directrices are the vertical lines $$x=\pm\dfrac{a}{e}$$, so the distance between these directrices is $$2\dfrac{a}{e}$$. Finally, the length of the latus rectum (the focal chord perpendicular to the major axis) is given by the formula $$L=\dfrac{2b^{2}}{a}$$.

Now we translate the numerical data of the problem into equations. The distance between the foci is given as $$6$$, so

$$2c = 6 \;\;\Longrightarrow\;\; c = 3.$$

The distance between the directrices is given as $$12$$, therefore

$$2\dfrac{a}{e} = 12.$$

Since $$e=\dfrac{c}{a}$$, we can write $$\dfrac{a}{e} = \dfrac{a}{\tfrac{c}{a}} = \dfrac{a^{2}}{c}.$$ Substituting this in the previous relation, we get

$$2\left(\dfrac{a^{2}}{c}\right)=12.$$

Dividing both sides by $$2$$ yields

$$\dfrac{a^{2}}{c}=6.$$

Now we substitute the already known value $$c=3$$:

$$\dfrac{a^{2}}{3}=6 \;\;\Longrightarrow\;\; a^{2}=18 \;\;\Longrightarrow\;\; a=\sqrt{18}=3\sqrt{2}.$$

Next, using $$c^{2}=a^{2}-b^{2}$$ we find $$b$$. We have

$$b^{2}=a^{2}-c^{2}=18-9=9 \;\;\Longrightarrow\;\; b=3.$$

With $$a$$ and $$b$$ known, we can compute the length of the latus rectum:

$$L=\dfrac{2b^{2}}{a}=\dfrac{2(9)}{3\sqrt{2}}=\dfrac{18}{3\sqrt{2}}=\dfrac{6}{\sqrt{2}}.$$

Rationalising the denominator gives

$$L=\dfrac{6}{\sqrt{2}}\times\dfrac{\sqrt{2}}{\sqrt{2}}=\dfrac{6\sqrt{2}}{2}=3\sqrt{2}.$$

Hence, the correct answer is Option B.

Let us take the ellipse in its standard (centre-origin, major axis on the X-axis) form

$$\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1,\qquad a>b>0.$$

For this ellipse we recall the following facts:

• The distance of each focus from the centre is $$c,$$ where $$c^{2}=a^{2}-b^{2}.$$

• The eccentricity is defined by $$e=\dfrac{c}{a},$$ so that $$e^{2}=\dfrac{c^{2}}{a^{2}}=\dfrac{a^{2}-b^{2}}{a^{2}}=1-\dfrac{b^{2}}{a^{2}}.$$

• The latus rectum corresponding to the focus $$(c,0)$$ is the line $$x=c,$$ and its two end-points on the ellipse are

$$\left(c,\;\;\frac{b^{2}}{a}\right)\quad\text{and}\quad\left(c,\;-\frac{b^{2}}{a}\right).$$

We choose the upper end of the latus rectum, namely

$$P\bigl(c,\;y_{1}\bigr)=\left(c,\;\frac{b^{2}}{a}\right).$$

The slope of the tangent at any point $$(x,y)$$ of the ellipse is obtained by implicit differentiation of the defining equation:

$$\frac{d}{dx}\!\left(\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}\right)=\frac{d}{dx}(1) \;\Longrightarrow\;\frac{2x}{a^{2}}+\frac{2y}{b^{2}}\frac{dy}{dx}=0,$$

hence

$$\frac{dy}{dx}=m_{t}=-\frac{b^{2}x}{a^{2}y}.$$

Therefore the slope of the normal is the negative reciprocal:

$$m_{n}=+\frac{a^{2}y}{b^{2}x}.$$

Evaluating this at the point $$P(c,\;b^{2}/a)$$ we get

$$m_{n}=\frac{a^{2}\,(b^{2}/a)}{b^{2}\,c}=\frac{a}{c}.$$

Thus the equation of the normal at $$P$$ is

$$y-\frac{b^{2}}{a}=\frac{a}{c}\Bigl(x-c\Bigr).$$

According to the statement of the problem, this normal line passes through an extremity of the minor axis. The extremities of the minor axis are $$(0,b)$$ and $$(0,-b).$$ Substituting $$(0,-b)$$ (we shall see that this choice gives a consistent, positive value of $$b$$) in the equation of the normal, we have

$$-b-\frac{b^{2}}{a}=\frac{a}{c}\bigl(0-c\bigr)=\frac{a}{c}(-c)=-a.$$

Collecting like terms:

$$-b-\frac{b^{2}}{a}+a=0.$$

Multiplying every term by $$a$$ to clear the denominator,

$$-ab-b^{2}+a^{2}=0,$$

or equivalently

$$a^{2}-ab-b^{2}=0.$$

Now we wish to express everything in terms of the single variable $$e.$$ For this purpose set

$$k=\frac{b}{a}\quad\bigl(\;0<k<1\;\bigr).$$

Dividing the last obtained relation by $$a^{2}$$ gives

$$1-k-k^{2}=0,$$

which can be written as

$$k^{2}+k-1=0.$$

Next we relate $$k$$ to $$e.$$ From the basic identity quoted earlier,

$$e^{2}=1-\frac{b^{2}}{a^{2}}=1-k^{2}.$$

Because $$k^{2}=1-k$$ from the quadratic immediately above, we substitute:

$$e^{2}=1-(1-k)=k.$$

Thus we have obtained

$$k=e^{2}.$$

Returning to the quadratic satisfied by $$k,$$ namely $$k^{2}+k-1=0,$$ we now replace $$k$$ by $$e^{2}:$$

$$\bigl(e^{2}\bigr)^{2}+e^{2}-1=0.$$

Simplifying,

$$e^{4}+e^{2}-1=0.$$

Hence, the correct answer is Option C.

We have to find the point $$P(x,\,y)$$ lying on the curve $$4x^2 + 5y^2 = 20$$ that is farthest from the fixed point $$Q(0,\,-4)$$. Instead of the distance itself, we maximise the square of the distance, because the square reaches its maximum at the same point and is easier to handle algebraically.

Let us denote the square of the distance by

$$D^2 \;=\; (x-0)^2 \;+\; (y+4)^2 \;=\; x^2 + (y+4)^2.$$

The point $$P(x,\,y)$$ must satisfy the given constraint

$$4x^2 + 5y^2 = 20.$$

To maximise $$D^2$$ under this constraint we use the method of Lagrange multipliers. We set up

$$f(x,y) = x^2 + (y+4)^2,$$

and introduce the function

$$g(x,y) = 4x^2 + 5y^2 - 20 = 0.$$

The gradient equations are

$$\nabla f \;=\; \lambda \,\nabla g.$$

First compute the partial derivatives:

$$\frac{\partial f}{\partial x} = 2x, \qquad \frac{\partial f}{\partial y} = 2(y+4),$$

$$\frac{\partial g}{\partial x} = 8x, \qquad \frac{\partial g}{\partial y} = 10y.$$

Equating corresponding components, we obtain two equations:

$$2x = \lambda\,(8x) \quad\Longrightarrow\quad 2x = 8\lambda x,$$

$$2(y+4) = \lambda\,(10y) \quad\Longrightarrow\quad 2(y+4) = 10\lambda y.$$

From the first equation, two possibilities arise:

(i) $$x = 0,$$ (ii) $$x \neq 0,$$ in which case we may cancel $$x$$ and get $$\lambda = \dfrac14.$$

Case (i) $$x = 0$$.

Substituting into the constraint,

$$4(0)^2 + 5y^2 = 20 \;\Longrightarrow\; 5y^2 = 20 \;\Longrightarrow\; y^2 = 4 \;\Longrightarrow\; y = \pm 2.$$

Now compute the squared distances:

For $$y = 2\!:$$

$$D^2 = 0^2 + (2+4)^2 = 6^2 = 36.$$

For $$y = -2\!:$$

$$D^2 = 0^2 + (-2+4)^2 = 2^2 = 4.$$

Case (ii) $$x \neq 0,\;\lambda = \dfrac14$$.

Insert $$\lambda = \dfrac14$$ into the second Lagrange equation:

$$2(y+4) = 10\Bigl(\dfrac14\Bigr) y = \dfrac{10y}{4} = \dfrac{5y}{2}.$$

Multiply both sides by 2:

$$4(y+4) = 5y \;\Longrightarrow\; 4y + 16 = 5y \;\Longrightarrow\; 16 = y.$$

Now use the constraint:

$$4x^2 + 5(16)^2 = 20 \;\Longrightarrow\; 4x^2 + 5\cdot256 = 20 \;\Longrightarrow\; 4x^2 + 1280 = 20 \;\Longrightarrow\; 4x^2 = -1260,$$

which is impossible for real $$x$$. Hence no admissible point arises from this case.

Therefore the only valid candidates are the two points with $$x = 0$$ and $$y = \pm 2$$, among which the farthest one is $$P(0,\,2)$$ giving

$$PQ^2 = 36.$$

Hence, the correct answer is Option A.

We have an ellipse whose equation is $$\dfrac{x^2}{25} + \dfrac{y^2}{b^2} = 1,\; (b < 5).$$

For any ellipse of the form $$\dfrac{x^2}{a^2} + \dfrac{y^2}{b^2} = 1$$ with its major axis along the $$x$$-axis, the standard results are

$$a^2 = \text{denominator of }x^2,\quad b^2 = \text{denominator of }y^2,$$

$$c^2 = a^2 - b^2,\quad e = \dfrac{c}{a},$$

where $$c$$ is the semi-focal distance and $$e$$ is the eccentricity.

Comparing, we identify $$a^2 = 25$$ and $$b^2 = b^2$$ itself. Therefore

$$c_1^2 = a^2 - b^2 = 25 - b^2,$$

so $$c_1 = \sqrt{25 - b^2}.$$

Hence the eccentricity of the ellipse is

$$e_1 = \dfrac{c_1}{a} = \dfrac{\sqrt{25 - b^2}}{5}.$$

Next we have a hyperbola whose equation is $$\dfrac{x^2}{16} - \dfrac{y^2}{b^2} = 1.$$

For any hyperbola of the form $$\dfrac{x^2}{a^2} - \dfrac{y^2}{b^2} = 1,$$ the corresponding formulas are

$$a^2 = \text{denominator of }x^2,\quad b^2 = \text{denominator of }y^2,$$

$$c^2 = a^2 + b^2,\quad e = \dfrac{c}{a},$$

because in a hyperbola the relationship involves a plus sign in $$c^2 = a^2 + b^2.$$

Here $$a^2 = 16$$ and again $$b^2 = b^2.$$ Thus

$$c_2^2 = a^2 + b^2 = 16 + b^2,$$

so $$c_2 = \sqrt{16 + b^2}.$$

The eccentricity of the hyperbola is therefore

$$e_2 = \dfrac{c_2}{a} = \dfrac{\sqrt{16 + b^2}}{4}.$$

The condition given in the problem is $$e_1 e_2 = 1.$$ Substituting the expressions we have just derived,

$$\left(\dfrac{\sqrt{25 - b^2}}{5}\right) \left(\dfrac{\sqrt{16 + b^2}}{4}\right) = 1.$$

Multiplying the numerators and denominators separately we get

$$\dfrac{\sqrt{(25 - b^2)(16 + b^2)}}{20} = 1.$$

Now multiply both sides by $$20$$:

$$\sqrt{(25 - b^2)(16 + b^2)} = 20.$$

To remove the square root we square both sides:

$$(25 - b^2)(16 + b^2) = 400.$$

Expanding the left-hand side step by step,

$$25 \times 16 + 25 b^2 - 16 b^2 - b^4 = 400.$$

The product $$25 \times 16 = 400,$$ so we have

$$400 + 25 b^2 - 16 b^2 - b^4 = 400.$$

Combining the like terms in $$b^2$$ gives

$$400 + 9 b^2 - b^4 = 400.$$

Subtract $$400$$ from both sides:

$$9 b^2 - b^4 = 0.$$

Factor out $$b^2$$:

$$b^2 (9 - b^2) = 0.$$

The factor $$b^2 = 0$$ is inadmissible because the denominators in the original equations would vanish. Therefore,

$$9 - b^2 = 0 \quad \Longrightarrow \quad b^2 = 9.$$

Since $$b > 0$$ and the problem states $$b < 5,$$ we choose

$$b = 3.$$

Now we can compute the quantities asked for. First, the distance between the two foci of the ellipse is

$$\alpha = 2 c_1 = 2 \sqrt{25 - b^2} = 2 \sqrt{25 - 9} = 2 \times 4 = 8.$$

Next, the distance between the two foci of the hyperbola is

$$\beta = 2 c_2 = 2 \sqrt{16 + b^2} = 2 \sqrt{16 + 9} = 2 \times 5 = 10.$$

Hence the ordered pair is $$(\alpha, \beta) = (8, 10).$$

Looking at the options, this matches Option A.

Hence, the correct answer is Option A.

We have an ellipse whose standard equation is $$\dfrac{x^{2}}{a^{2}}+\dfrac{y^{2}}{b^{2}}=1$$ with the major axis along the x-direction and the condition $$a>b\;.$$

The question gives two independent pieces of information:

1. The length of the latus-rectum is 10.
2. The eccentricity is the greatest value attained by the quadratic function $$\phi(t)=\dfrac{5}{12}+t-t^{2}\,.$$

We shall translate each of these statements into equations involving $$a,\;b$$ and then solve for $$a^{2}+b^{2}.$$

Length of the latus-rectum.
For an ellipse centred at the origin, the length of the latus-rectum (the complete chord through a focus perpendicular to the major axis) is given by the well-known formula

$$\text{Length of latus-rectum}= \dfrac{2b^{2}}{a}\,.$$

The problem states that this length equals 10, so we write

$$\dfrac{2b^{2}}{a}=10 \;\Longrightarrow\; b^{2}=5a.$$

We shall remember this linear relation between $$b^{2}$$ and $$a$$ for later substitution.

Maximum value of the given quadratic and the eccentricity.
The eccentricity of the ellipse, denoted $$e,$$ is declared to be the maximum value of $$\phi(t)=\dfrac{5}{12}+t-t^{2}.$$

First we recall the standard result for a quadratic $$f(t)=At^{2}+Bt+C$$ with $$A\lt 0:$$ the maximum occurs at

$$t=-\dfrac{B}{2A}$$

and the corresponding maximum value is obtained by substituting this $$t$$ back into the quadratic.

In the present case we have $$A=-1,\;B=1,\;C=\dfrac{5}{12}.$$ Hence

$$t_{\text{max}}=-\dfrac{B}{2A}=-\dfrac{1}{2(-1)}=\dfrac12.$$

Substituting $$t=\dfrac12$$ into $$\phi(t)$$ gives

$$\phi_{\text{max}}=\dfrac{5}{12}+\dfrac12-\left(\dfrac12\right)^{2} =\dfrac{5}{12}+\dfrac12-\dfrac14 =\dfrac{5}{12}+\dfrac{6}{12}-\dfrac{3}{12} =\dfrac{8}{12} =\dfrac23.$$

Therefore the eccentricity is

$$e=\dfrac23.$$

Relating $$a$$ and $$b$$ using the eccentricity.
For an ellipse with semimajor axis $$a$$ and semiminor axis $$b,$$ the eccentricity is defined by

$$e=\sqrt{1-\dfrac{b^{2}}{a^{2}}}\,.$$

Squaring both sides, we have

$$e^{2}=1-\dfrac{b^{2}}{a^{2}} \;\Longrightarrow\; \dfrac{b^{2}}{a^{2}}=1-e^{2}.$$

Since $$e=\dfrac23,$$ we compute

$$e^{2}=\left(\dfrac23\right)^{2}=\dfrac49,$$ so

$$\dfrac{b^{2}}{a^{2}}=1-\dfrac49=\dfrac59.$$

This yields the quadratic relation

$$b^{2}=\dfrac59\,a^{2}.$$

Solving simultaneously for $$a$$ and $$b.$$
We have already obtained a linear relation $$b^{2}=5a$$ from the latus-rectum condition. Setting this equal to the quadratic relation just found, we write

$$5a=\dfrac59\,a^{2}.$$

Dividing both sides by 5 gives

$$a=\dfrac19\,a^{2}.$$

Because $$a\neq0,$$ we may divide by $$a$$ to obtain

$$1=\dfrac19\,a \;\Longrightarrow\; a=9.$$

With $$a$$ now known, we return to $$b^{2}=5a$$ to find $$b^{2}:$$

$$b^{2}=5a=5\times9=45.$$

Computing $$a^{2}+b^{2}.$$
We finally evaluate

$$a^{2}+b^{2}=9^{2}+45=81+45=126.$$

Hence, the correct answer is Option C.

We have the ellipse $$2x^{2}+y^{2}=1$$ and the straight line $$y=mx$$. Putting $$y=mx$$ in the equation of the ellipse gives the co-ordinates of their point of intersection P:

$$2x^{2}+(mx)^{2}=1 \quad\Longrightarrow\quad (2+m^{2})x^{2}=1 \;\Longrightarrow\;x=\dfrac{1}{\sqrt{\,2+m^{2}}}.$$

Because the point lies in the first quadrant, $$x>0,\;y>0,$$ so

$$P\left(\dfrac{1}{\sqrt{\,2+m^{2}}},\;\dfrac{m}{\sqrt{\,2+m^{2}}}\right).$$

The slope of the tangent to the ellipse is obtained by implicit differentiation. Differentiating $$2x^{2}+y^{2}=1$$ gives

$$4x+2y\dfrac{dy}{dx}=0 \quad\Longrightarrow\quad \dfrac{dy}{dx}=-\dfrac{2x}{y}.$$

Therefore, at P

$$\text{slope of tangent}=m_{\text{tan}}=-\dfrac{2x_{P}}{y_{P}} =-\dfrac{2}{m}.$$

Since the normal is perpendicular to the tangent,

$$m_{\text{tan}}\;m_{\text{norm}}=-1 \;\Longrightarrow\; \left(-\dfrac{2}{m}\right)m_{\text{norm}}=-1 \;\Longrightarrow\; m_{\text{norm}}=\dfrac{m}{2}.$$

The normal at P is therefore

$$y-\dfrac{m}{\sqrt{\,2+m^{2}}} =\dfrac{m}{2}\!\left(x-\dfrac{1}{\sqrt{\,2+m^{2}}}\right).$$

This normal meets the x-axis at $$\!\left(-\dfrac{1}{3\sqrt{2}},\,0\right)\!.$$ Putting $$y=0$$ in the equation of the normal and letting $$x=x_{i}$$ gives

$$0-\dfrac{m}{\sqrt{\,2+m^{2}}} =\dfrac{m}{2}\!\left(x_{i}-\dfrac{1}{\sqrt{\,2+m^{2}}}\right).$$

Dividing by $$m\;(m\neq0)$$ and multiplying by 2, we get

$$-\dfrac{2}{\sqrt{\,2+m^{2}}}=x_{i}-\dfrac{1}{\sqrt{\,2+m^{2}}} \;\Longrightarrow\; x_{i}=-\dfrac{1}{\sqrt{\,2+m^{2}}}.$$

But the given x-intercept is $$-\dfrac{1}{3\sqrt{2}},$$ so

$$-\dfrac{1}{\sqrt{\,2+m^{2}}}=-\dfrac{1}{3\sqrt{2}} \;\Longrightarrow\; \sqrt{\,2+m^{2}}=3\sqrt{2} \;\Longrightarrow\; 2+m^{2}=18 \;\Longrightarrow\; m^{2}=16 \;\Longrightarrow\; m=4\;(\text{positive for first quadrant}).$$

Now we find the y-intercept. Put $$x=0$$ in the normal:

$$y-\dfrac{m}{\sqrt{\,2+m^{2}}} =\dfrac{m}{2}\!\left(0-\dfrac{1}{\sqrt{\,2+m^{2}}}\right) =-\dfrac{m}{2}\cdot\dfrac{1}{\sqrt{\,2+m^{2}}}.$$

Hence

$$y=\dfrac{m}{\sqrt{\,2+m^{2}}}-\dfrac{m}{2}\cdot\dfrac{1}{\sqrt{\,2+m^{2}}} =\dfrac{m}{\sqrt{\,2+m^{2}}}\left(1-\dfrac12\right) =\dfrac{m}{2\sqrt{\,2+m^{2}}}.$$

Substituting $$m=4$$ and $$\sqrt{\,2+m^{2}}=\sqrt{18}=3\sqrt{2},$$ we obtain

$$\beta=\dfrac{4}{2\cdot3\sqrt{2}} =\dfrac{2}{3\sqrt{2}} =\dfrac{\sqrt{2}}{3}.$$

Hence, the correct answer is Option D.

We are told that the line $$x = 4$$ is a directrix of an ellipse whose centre is the origin and whose eccentricity is $$\dfrac12$$. For an ellipse centred at the origin with its major axis along the $$x$$-axis, the standard form is $$\frac{x^{2}}{a^{2}} + \frac{y^{2}}{b^{2}} = 1,$$ and its two directrices are $$x = \frac{a^{2}}{c}\quad\text{and}\quad x = -\frac{a^{2}}{c},$$ where $$c$$ is the distance from the centre to either focus.

The eccentricity is defined as $$e = \dfrac{c}{a}$$. We have $$e = \frac12 \;\Longrightarrow\; c = \frac{a}{2}.$$ For the given directrix $$x = 4$$ we equate $$\frac{a^{2}}{c} = 4.$$ Substituting $$c = \dfrac{a}{2}$$ gives $$\frac{a^{2}}{a/2} = 4 \;\Longrightarrow\; 2a = 4 \;\Longrightarrow\; a = 2.$$ So $$c = \frac{a}{2} = \frac{2}{2} = 1.$$

Using $$b^{2} = a^{2} - c^{2}$$, we obtain $$b^{2} = 2^{2} - 1^{2} = 4 - 1 = 3 \;\Longrightarrow\; b = \sqrt3.$$ Hence the equation of the ellipse is $$\frac{x^{2}}{4} + \frac{y^{2}}{3} = 1.$$

The point $$P(1,\beta)$$ lies on the ellipse with $$\beta \gt 0$$, so we substitute $$x = 1,\; y = \beta$$: $$\frac{1^{2}}{4} + \frac{\beta^{2}}{3} = 1 \;\Longrightarrow\; \frac14 + \frac{\beta^{2}}{3} = 1 \;\Longrightarrow\; \frac{\beta^{2}}{3} = 1 - \frac14 = \frac34 \;\Longrightarrow\; \beta^{2} = 3 \times \frac34 = \frac{9}{4} \;\Longrightarrow\; \beta = \frac32 \;(\text{since } \beta \gt 0).$$ Thus $$P\bigl(1,\tfrac32\bigr).$$

To find the normal at $$P$$ we first need the slope of the tangent. Differentiating $$\frac{x^{2}}{4} + \frac{y^{2}}{3} = 1$$ implicitly with respect to $$x$$ gives $$\frac{x}{2} + \frac{2y}{3}\,\frac{dy}{dx} = 0 \;\Longrightarrow\; \frac{dy}{dx} = -\frac{3x}{4y}.$$ At $$P(1,\tfrac32)$$, $$m_{\text{tangent}} = -\frac{3 \times 1}{4 \times (3/2)} = -\frac{3}{6} = -\frac12.$$ The slope of the normal is the negative reciprocal: $$m_{\text{normal}} = 2.$$

The normal through $$P(1,\tfrac32)$$ is therefore $$y - \frac32 = 2\,(x - 1).$$ Expanding, $$y - \frac32 = 2x - 2 \;\Longrightarrow\; y = 2x - 2 + \frac32 = 2x - \frac12.$$ Multiplying by $$2$$ to clear the fraction, $$2y = 4x - 1 \;\Longrightarrow\; 4x - 2y = 1.$$

This matches Option D.

Hence, the correct answer is Option D.

We begin with the standard form of an ellipse whose centre is at the origin and whose major axis lies along the x-axis:

$$\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1,\qquad a>b>0.$$

The minor axis is along the y-axis and its total length is $$2b.$$ We are told that this length equals $$\dfrac{4}{\sqrt{3}},$$ so

$$2b=\frac{4}{\sqrt{3}}\;\Longrightarrow\;b=\frac{2}{\sqrt{3}}.$$

Next, the line $$x+6y=8$$ is tangent to the ellipse. To use the tangent condition, we first rewrite the line in slope-intercept form:

$$x+6y=8\;\Longrightarrow\;6y=-x+8\;\Longrightarrow\;y=-\frac{1}{6}x+\frac{4}{3}.$$

Thus the slope is $$m=-\dfrac{1}{6}$$ and the y-intercept is $$c=\dfrac{4}{3}.$$

The well-known tangent condition for an ellipse $$\dfrac{x^{2}}{a^{2}}+\dfrac{y^{2}}{b^{2}}=1$$ says:

For a line of the form $$y=mx+c$$ to touch the ellipse, we must have $$c^{2}=a^{2}m^{2}+b^{2}.$$

Substituting $$m=-\dfrac{1}{6},\;c=\dfrac{4}{3},\;b=\dfrac{2}{\sqrt{3}},$$ we get

$$\left(\frac{4}{3}\right)^{2}=a^{2}\left(-\frac{1}{6}\right)^{2}+\left(\frac{2}{\sqrt{3}}\right)^{2}.$$

Working out each term:

$$\frac{16}{9}=a^{2}\left(\frac{1}{36}\right)+\frac{4}{3}.$$

Now we isolate the term containing $$a^{2}$$:

$$\frac{16}{9}-\frac{4}{3}=a^{2}\left(\frac{1}{36}\right).$$

Because $$\frac{4}{3}=\frac{12}{9},$$ we have

$$\frac{16}{9}-\frac{12}{9}=\frac{4}{9}=\frac{a^{2}}{36}.$$

Multiplying both sides by $$36$$ gives

$$a^{2}=36\left(\frac{4}{9}\right)=4\times4=16.$$

So $$a=4.$$

The eccentricity $$e$$ of an ellipse with major axis along the x-axis is defined by the relation

$$e^{2}=1-\frac{b^{2}}{a^{2}}.$$

Substituting $$a^{2}=16$$ and $$b^{2}=\left(\frac{2}{\sqrt{3}}\right)^{2}=\frac{4}{3},$$ we obtain

$$e^{2}=1-\frac{\dfrac{4}{3}}{16}=1-\frac{4}{48}=1-\frac{1}{12}=\frac{11}{12}.$$

Taking the positive square root (since eccentricity is positive),

$$e=\sqrt{\frac{11}{12}}=\frac{\sqrt{11}}{\sqrt{12}}=\frac{\sqrt{11}}{2\sqrt{3}}=\frac{1}{2}\sqrt{\frac{11}{3}}.$$

Hence, the correct answer is Option A.

We have the ellipse

$$\frac{x^{2}}4+\frac{y^{2}}2=1$$

so that

$$a^{2}=4,\qquad a=2,\qquad b^{2}=2,\qquad b=\sqrt2.$$

The eccentricity is

$$e=\sqrt{1-\frac{b^{2}}{a^{2}}}=\sqrt{1-\frac{2}{4}}=\sqrt{\frac12}=\frac1{\sqrt2},$$

hence the distance of each focus from the centre is

$$c=ae=2\cdot\frac1{\sqrt2}=\sqrt2.$$

Taking the focus on the positive $$x$$-axis, we write

$$S\bigl(c,0\bigr)=\bigl(\sqrt2,0\bigr).$$

Any point of the ellipse can be parameterised as

$$T\bigl(x_{1},y_{1}\bigr)=\bigl(a\cos\theta,\;b\sin\theta\bigr)=\bigl(2\cos\theta,\;\sqrt2\sin\theta\bigr).$$

The standard tangent at this point is (first state the formula)

$$\frac{x\cos\theta}{a}+\frac{y\sin\theta}{b}=1.$$

Substituting the present values of $$a$$ and $$b$$, the tangent becomes

$$\frac{x\cos\theta}{2}+\frac{y\sin\theta}{\sqrt2}=1.$$ Writing it in the form $$Ax+By+C=0$$ we have

$$A=\frac{\cos\theta}{2},\qquad B=\frac{\sin\theta}{\sqrt2},\qquad C=-1.$$

Let the required foot of the perpendicular from the focus $$S$$ to this tangent be

$$P(h,k).$$

Because $$SP$$ is perpendicular to the tangent, the vector $$\overrightarrow{SP}$$ must be parallel to the normal vector of the tangent, namely $$(A,B)$$. Thus we can write

$$\frac{h-c}{A}=\frac{k-0}{B}=\lambda\quad(\text{say}).$$

This gives

$$h-c=\lambda A=\lambda\frac{\cos\theta}{2},\qquad k=\lambda B=\lambda\frac{\sin\theta}{\sqrt2}.$$ So $$h=c+\lambda\frac{\cos\theta}{2},\qquad k=\lambda\frac{\sin\theta}{\sqrt2}.$$

Next, because $$P$$ actually lies on the tangent, substitute $$(h,k)$$ in the tangent equation:

$$\frac{h\cos\theta}{2}+\frac{k\sin\theta}{\sqrt2}=1.$$ Putting the above expressions for $$h$$ and $$k$$ we obtain

$$\frac{\bigl(c+\lambda\frac{\cos\theta}{2}\bigr)\cos\theta}{2} +\frac{\bigl(\lambda\frac{\sin\theta}{\sqrt2}\bigr)\sin\theta}{\sqrt2}=1.$$ Simplifying, $$\frac{c\cos\theta}{2}+\lambda\!\left(\frac{\cos^{2}\theta}{4} +\frac{\sin^{2}\theta}{2}\right)=1.$$

Define the quantity

$$D=\frac{\cos^{2}\theta}{4}+\frac{\sin^{2}\theta}{2}.$$

Then we can solve for $$\lambda$$:

$$\lambda=\frac{1-\dfrac{c\cos\theta}{2}}{D}.$$ Substituting this value of $$\lambda$$ back into $$h$$ and $$k$$ gives

$$h=c+\frac{\cos\theta}{2}\cdot\frac{1-\dfrac{c\cos\theta}{2}}{D},\qquad k=\frac{\sin\theta}{\sqrt2}\cdot\frac{1-\dfrac{c\cos\theta}{2}}{D}.$$

Now we calculate $$h^{2}+k^{2}$$. First note that

$$h^{2}+k^{2} =c^{2}+2c\cdot\frac{\cos\theta}{2}\cdot\frac{1-\dfrac{c\cos\theta}{2}}{D} +\left(\frac{\cos^{2}\theta}{4}+\frac{\sin^{2}\theta}{2}\right) \!\!\left(\frac{1-\dfrac{c\cos\theta}{2}}{D}\right)^{2}.$$

The factor in the last bracket is precisely $$D$$, so the last term equals $$\frac{\bigl(1-\dfrac{c\cos\theta}{2}\bigr)^{2}}{D}.$$

Hence

$$h^{2}+k^{2} =c^{2}+\frac{2c\cos\theta}{2}\cdot\frac{1-\dfrac{c\cos\theta}{2}}{D} +\frac{\bigl(1-\dfrac{c\cos\theta}{2}\bigr)^{2}}{D}$$ $$ =c^{2}+\frac{1-\dfrac{c^{2}\cos^{2}\theta}{4}}{D}. $$

But by direct calculation one checks that

$$D=\frac{1}{2}-\frac{c^{2}\cos^{2}\theta}{8},$$ so that $$\frac{1-\dfrac{c^{2}\cos^{2}\theta}{4}}{D}=4.$$ Therefore

$$h^{2}+k^{2}=c^{2}+4.$$ Recalling that $$c^{2}=a^{2}-b^{2}$$, we find $$h^{2}+k^{2}=a^{2}-b^{2}+4=a^{2}.$$ But $$a=2$$, hence

$$h^{2}+k^{2}=4.$$

Thus every foot of the perpendicular from either focus to any tangent of the ellipse lies on the circle

$$x^{2}+y^{2}=4.$$

Conversely, for every point on this circle there exists such a tangent, so the locus is exactly that circle.

We now inspect the given options.

• Option A: $$(-2,\sqrt3)$$ gives $$4+3=7\neq4.$$
• Option B: $$(-1,\sqrt2)$$ gives $$1+2=3\neq4.$$
• Option C: $$(-1,\sqrt3)$$ gives $$1+3=4,$$ which satisfies the locus.
• Option D: $$(1,2)$$ gives $$1+4=5\neq4.$$

Only Option C satisfies $$x^{2}+y^{2}=4$$.

Hence, the correct answer is Option C.

We have the hyperbola

$$x^{2}-y^{2}\sec^{2}\theta = 10$$

and the ellipse

$$x^{2}\sec^{2}\theta + y^{2}=5,$$

where $$\theta\in\left(0,\dfrac{\pi}{2}\right).$$

First we rewrite the hyperbola in standard form. Dividing by $$10$$ gives

$$\frac{x^{2}}{10}-\frac{y^{2}\sec^{2}\theta}{10}=1.$$

Comparing with the standard form $$\dfrac{x^{2}}{a^{2}}-\dfrac{y^{2}}{b^{2}}=1,$$ we identify

$$a^{2}=10,\qquad \frac{1}{b^{2}}=\frac{\sec^{2}\theta}{10}\;\Longrightarrow\; b^{2}=\frac{10}{\sec^{2}\theta}=10\cos^{2}\theta.$$

The eccentricity formula for a hyperbola is $$e_{h}^{2}=1+\dfrac{b^{2}}{a^{2}}.$$ Substituting $$a^{2}=10$$ and $$b^{2}=10\cos^{2}\theta$$, we get

$$e_{h}^{2}=1+\frac{10\cos^{2}\theta}{10}=1+\cos^{2}\theta,$$

so

$$e_{h}=\sqrt{1+\cos^{2}\theta}.$$

Now we put the ellipse into standard form. Dividing $$x^{2}\sec^{2}\theta + y^{2}=5$$ by $$5$$ yields

$$\frac{x^{2}\sec^{2}\theta}{5}+\frac{y^{2}}{5}=1.$$

Thus

$$\frac{x^{2}}{5\cos^{2}\theta}+\frac{y^{2}}{5}=1.$$

Here the larger denominator is $$5,$$ so

$$a^{2}=5,\qquad b^{2}=5\cos^{2}\theta,\qquad a=\sqrt5.$$

For an ellipse the eccentricity satisfies $$e_{e}^{2}=1-\dfrac{b^{2}}{a^{2}}.$$ Hence

$$e_{e}^{2}=1-\frac{5\cos^{2}\theta}{5}=1-\cos^{2}\theta=\sin^{2}\theta,$$

giving

$$e_{e}=\sin\theta.$$

According to the condition in the question,

$$e_{h}=\sqrt5\,e_{e}.$$ Substituting $$e_{h}=\sqrt{1+\cos^{2}\theta}$$ and $$e_{e}=\sin\theta,$$ we obtain

$$\sqrt{1+\cos^{2}\theta}=\sqrt5\,\sin\theta.$$

Squaring both sides:

$$1+\cos^{2}\theta=5\sin^{2}\theta.$$

Using $$\sin^{2}\theta=1-\cos^{2}\theta,$$ we get

$$1+\cos^{2}\theta=5(1-\cos^{2}\theta).$$

Expanding and collecting like terms:

$$1+\cos^{2}\theta=5-5\cos^{2}\theta$$ $$\Longrightarrow\;1+\cos^{2}\theta-5+5\cos^{2}\theta=0$$ $$\Longrightarrow\;-4+6\cos^{2}\theta=0$$ $$\Longrightarrow\;6\cos^{2}\theta=4$$ $$\Longrightarrow\;\cos^{2}\theta=\frac{4}{6}=\frac{2}{3}.$$

Since $$0<\theta<\dfrac{\pi}{2},$$ we have

$$\cos\theta=\sqrt{\frac{2}{3}},\qquad \sin\theta=\sqrt{1-\frac{2}{3}}=\sqrt{\frac{1}{3}}=\frac{1}{\sqrt3}.$$

Now we compute the length of the latus rectum of the ellipse. For an ellipse the length of the latus rectum is given by

$$\text{Latus Rectum}= \frac{2b^{2}}{a}.$$

We already have $$b^{2}=5\cos^{2}\theta=5\cdot\frac{2}{3}=\frac{10}{3}$$ and $$a=\sqrt5.$$ Therefore

$$\text{Latus Rectum}= \frac{2\left(\dfrac{10}{3}\right)}{\sqrt5}=\frac{20}{3\sqrt5}.$$

Rationalising the denominator:

$$\frac{20}{3\sqrt5}\times\frac{\sqrt5}{\sqrt5}=\frac{20\sqrt5}{3\cdot5}=\frac{4\sqrt5}{3}.$$

Hence, the correct answer is Option D.

We are given the ellipse $$\dfrac{x^{2}}{a^{2}}+\dfrac{y^{2}}{9}=1$$ and the straight line $$3x+4y=12\sqrt{2}$$. The line is said to be a tangent to the ellipse, and we have to find the distance between the foci of that ellipse.

For any ellipse $$\dfrac{x^{2}}{A^{2}}+\dfrac{y^{2}}{B^{2}}=1$$ the condition that a straight line $$lx+my=n$$ should touch (be tangent to) the ellipse is the well-known tangent condition

$$n^{2}=A^{2}l^{2}+B^{2}m^{2}.$$

In our case we can match the coefficients as follows:

$$l=3,\; m=4,\; n=12\sqrt{2},$$

and, comparing $$(A^{2},B^{2})$$ with the given ellipse, we have

$$A^{2}=a^{2},\quad B^{2}=9.$$

Now we substitute these four numbers into the tangent condition:

$$\bigl(12\sqrt{2}\bigr)^{2}=a^{2}(3)^{2}+9(4)^{2}.$$

Simplifying each term step by step:

Left side:

$$\bigl(12\sqrt{2}\bigr)^{2}=12^{2}\times 2=144\times 2=288.$$

Right side:

$$a^{2}(3)^{2}+9(4)^{2}=a^{2}\cdot 9+9\cdot 16=9a^{2}+144.$$

Equating the two simplified sides we get

$$288=9a^{2}+144.$$

Now we isolate $$9a^{2}$$ by subtracting $$144$$ from both sides:

$$288-144=9a^{2},$$

so

$$144=9a^{2}.$$

Dividing both sides by $$9$$ yields

$$a^{2}=16.$$

Thus the semi-major axis squared of the ellipse is $$16$$. We observe that $$a^{2}=16$$ is greater than $$b^{2}=9$$, hence the major axis is along the $$x$$-direction. For an ellipse whose major axis is along the $$x$$-direction the focal distance relation is

$$c^{2}=a^{2}-b^{2}.$$

Substituting $$a^{2}=16$$ and $$b^{2}=9$$ gives

$$c^{2}=16-9=7.$$

Taking the positive square root,

$$c=\sqrt{7}.$$

The distance between the two foci is twice this value:

$$2c=2\sqrt{7}.$$

Hence, the correct answer is Option A.

We consider the standard form of an ellipse whose centre is at the origin and whose major axis lies along the x-axis. In such a case the equation is

$$\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1,\qquad a>b>0.$$

The distance between the foci is $$2c$$ where, by definition of an ellipse, we have $$c^{2}=a^{2}-b^{2}.$$ The length of the minor axis is $$2b,$$ while the length of the (transverse) latus rectum is given by the standard formula

$$\text{Length of latus rectum}= \frac{2b^{2}}{a}.$$

According to the statement of the problem, the latus-rectum length is $$8$$ and the distance between the foci equals the length of the minor axis. Translating both facts into algebra, we write

$$\frac{2b^{2}}{a}=8 \quad\text{and}\quad 2c=2b.$$

The second equality simplifies immediately to

$$c=b.$$

But from the definition $$c^{2}=a^{2}-b^{2},$$ replacing $$c$$ by $$b$$ gives

$$b^{2}=a^{2}-b^{2}\quad\Longrightarrow\quad 2b^{2}=a^{2}.$$

Thus

$$a^{2}=2b^{2}\quad\Longrightarrow\quad a=\sqrt{2}\,b.$$

Now we use the first given condition, namely $$\dfrac{2b^{2}}{a}=8.$$ Substituting $$a=\sqrt{2}\,b$$ yields

$$\frac{2b^{2}}{\sqrt{2}\,b}=8.$$

Carrying out the division in the numerator and denominator,

$$\frac{2b^{2}}{\sqrt{2}\,b}=\frac{2b}{\sqrt{2}}=\frac{2b\sqrt{2}}{2}=b\sqrt{2},$$

so we have

$$b\sqrt{2}=8\quad\Longrightarrow\quad b=\frac{8}{\sqrt{2}}=4\sqrt{2}.$$

Squaring this value gives $$b^{2}=(4\sqrt{2})^{2}=16\cdot2=32.$$ Since $$a^{2}=2b^{2},$$ we obtain

$$a^{2}=2\cdot32=64\quad\Longrightarrow\quad a=8.$$

Therefore the explicit equation of the ellipse is

$$\frac{x^{2}}{64}+\frac{y^{2}}{32}=1.$$

To find which option lies on this ellipse, we substitute each point into the left side of the equation and see whether the value equals $$1.$$ Let us test each candidate:

Option A: $$(4\sqrt{2},\,2\sqrt{2}).$$ We have $$x^{2}= (4\sqrt{2})^{2}=32,\; y^{2}=(2\sqrt{2})^{2}=8.$$ Hence $$\frac{x^{2}}{64}+\frac{y^{2}}{32}= \frac{32}{64}+\frac{8}{32}=0.5+0.25=0.75\lt1,$$ so the point is inside the ellipse, not on it.

Option B: $$(4\sqrt{3},\,2\sqrt{2}).$$ Now $$x^{2}= (4\sqrt{3})^{2}=48,\; y^{2}=(2\sqrt{2})^{2}=8.$$ Thus $$\frac{x^{2}}{64}+\frac{y^{2}}{32}= \frac{48}{64}+\frac{8}{32}=0.75+0.25=1.$$ Because the sum equals $$1,$$ this point satisfies the ellipse’s equation exactly and therefore lies on the curve.

Option C: $$(4\sqrt{3},\,2\sqrt{3}).$$ Here $$x^{2}=48,\; y^{2}=(2\sqrt{3})^{2}=12.$$ Then $$\frac{x^{2}}{64}+\frac{y^{2}}{32}= \frac{48}{64}+\frac{12}{32}=0.75+0.375=1.125\gt1,$$ so the point is outside the ellipse.

Option D: $$(4\sqrt{2},\,2\sqrt{3}).$$ Now $$x^{2}=32,\; y^{2}=12,$$ giving $$\frac{x^{2}}{64}+\frac{y^{2}}{32}=0.5+0.375=0.875\lt1,$$ again inside the ellipse.

Only Option B satisfies the equation precisely.

Hence, the correct answer is Option B.

We have the ellipse whose canonical equation is $$\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1.$$

The line $$x-2y=12$$ is given to be a tangent to this ellipse at the point $$\left(3,\,-\frac{9}{2}\right).$$

First, we recall (state) the standard tangent-line formula for an ellipse. For the ellipse $$\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1,$$ the tangent at any point $$(x_{1},y_{1})$$ on the ellipse is

$$\frac{xx_{1}}{a^{2}}+\frac{yy_{1}}{b^{2}}=1.$$

Here the point of contact is $$(x_{1},y_{1})=\left(3,\,-\dfrac{9}{2}\right).$$ Substituting these coordinates into the tangent formula, we obtain

$$\frac{3x}{a^{2}}+\frac{\left(-\dfrac{9}{2}\right)y}{b^{2}}=1 \;\Longrightarrow\; \frac{3x}{a^{2}}-\frac{9y}{2b^{2}}=1.$$

This is the same straight line as the given tangent $$x-2y=12,$$ so both must represent exactly the same set of points in the plane. Two linear equations represent the same line if their corresponding coefficients are proportional. To make the comparison easy, we rewrite the given tangent with a right-hand side equal to $$1$$ (just like the equation above) by dividing every term by $$12$$:

$$\frac{x}{12}-\frac{2y}{12}=1 \;\Longrightarrow\; \frac{x}{12}-\frac{y}{6}=1.$$

Now we equate corresponding coefficients.

Coefficient of $$x:$$ $$\frac{3}{a^{2}}=\frac{1}{12}\quad\Longrightarrow\quad 3\cdot12=a^{2}\quad\Longrightarrow\quad a^{2}=36.$$

Coefficient of $$y:$$ $$-\frac{9}{2b^{2}}=-\frac{1}{6}\quad\Longrightarrow\quad\frac{9}{2b^{2}}=\frac{1}{6} \quad\Longrightarrow\quad 9\cdot6=2b^{2} \quad\Longrightarrow\quad 54=2b^{2} \quad\Longrightarrow\quad b^{2}=27.$$

We now know $$a^{2}=36,\; b^{2}=27,$$ and clearly $$a^{2}>b^{2},$$ so the major axis is along the $$x$$-direction.

For an ellipse with semi-major axis $$a$$ (along the $$x$$-axis) and semi-minor axis $$b,$$ the length of the latus rectum (denoted $$L$$) is given by the formula

$$L=\frac{2b^{2}}{a}.$$

Substituting $$b^{2}=27$$ and $$a=\sqrt{36}=6,$$ we get

$$L=\frac{2\,(27)}{6} =\frac{54}{6} =9\;\text{units}.$$

Hence, the correct answer is Option C.

We have the ellipse $$3x^{2}+4y^{2}=12$$ and a point $$P(x_{1},y_{1})$$ on it.

The line $$2x+y=4$$ is given to be parallel to the normal at $$P$$. The slope of this line is obtained by rewriting it in slope-intercept form:

$$y=-2x+4 \;\;\Longrightarrow\;\; \text{slope} = -2.$$

Recall the standard differentiation result: for any curve $$F(x,y)=0,$$ differentiating gives $$F_{x}+F_{y}\dfrac{dy}{dx}=0\quad\Longrightarrow\quad \dfrac{dy}{dx}=-\dfrac{F_{x}}{F_{y}}.$$ This $$\dfrac{dy}{dx}$$ is the slope of the tangent. The slope of the normal is its negative reciprocal.

For our ellipse,

$$F(x,y)=3x^{2}+4y^{2}-12=0,$$ so $$F_{x}=6x,\qquad F_{y}=8y.$$

Hence

$$\dfrac{dy}{dx}=-\dfrac{6x}{8y}=-\dfrac{3x}{4y} \quad\Longrightarrow\quad \text{Slope of normal }m_{n}=-\dfrac{1}{m_{t}}=\dfrac{4y}{3x}.$$

The normal is parallel to the line whose slope is $$-2,$$ therefore

$$\dfrac{4y_{1}}{3x_{1}}=-2 \;\;\Longrightarrow\;\; 4y_{1}=-6x_{1} \;\;\Longrightarrow\;\; x_{1}=-\dfrac{2}{3}y_{1}. \quad -(1)$$

Point $$P(x_{1},y_{1})$$ also lies on the ellipse, so

$$3x_{1}^{2}+4y_{1}^{2}=12.$$

Substituting the relation (1):

$$3\left(-\dfrac{2}{3}y_{1}\right)^{2}+4y_{1}^{2}=12$$ $$\Longrightarrow\; 3\left(\dfrac{4}{9}y_{1}^{2}\right)+4y_{1}^{2}=12$$ $$\Longrightarrow\; \dfrac{12}{9}y_{1}^{2}+4y_{1}^{2}=12$$ $$\Longrightarrow\; \dfrac{4}{3}y_{1}^{2}+4y_{1}^{2}=12$$ $$\Longrightarrow\; \dfrac{4+12}{3}y_{1}^{2}=12$$ $$\Longrightarrow\; \dfrac{16}{3}y_{1}^{2}=12$$ $$\Longrightarrow\; y_{1}^{2}=12\cdot\dfrac{3}{16}=\dfrac{36}{16}=\dfrac{9}{4}.$$

So

$$y_{1}=\pm\dfrac{3}{2},\qquad x_{1}=-\dfrac{2}{3}y_{1}\;\;\Longrightarrow\;\; x_{1}=\mp1.$$

The two candidate points are $$P_{1}\,(-1,\;3/2)\quad\text{and}\quad P_{2}\,(1,\;-3/2).$$

Next, the tangent at $$P$$ must pass through $$Q(4,4).$$ For the ellipse $$Ax^{2}+By^{2}=C,$$ the tangent at $$(x_{1},y_{1})$$ is $$Axx_{1}+Byy_{1}=C.$$ Here $$A=3,\;B=4,\;C=12,$$ so the tangent at $$P(x_{1},y_{1})$$ is

$$3xx_{1}+4yy_{1}=12.$$

Substituting $$Q(4,4)$$ gives the condition

$$3\cdot4\,x_{1}+4\cdot4\,y_{1}=12 \;\;\Longrightarrow\;\; 12x_{1}+16y_{1}=12 \;\;\Longrightarrow\;\; 3x_{1}+4y_{1}=3. \quad -(2)$$

We test both points:

For $$P_{1}(-1,3/2):$$ $$3(-1)+4\left(\dfrac{3}{2}\right)=-3+6=3,$$ so equation (2) is satisfied.

For $$P_{2}(1,-3/2):$$ $$3(1)+4\left(-\dfrac{3}{2}\right)=3-6=-3\neq3,$$ so $$P_{2}$$ is rejected.

Therefore $$P(-1,\;3/2).$$

Finally, the distance $$PQ$$ where $$Q(4,4)$$ is

$$PQ=\sqrt{(4-(-1))^{2}+\left(4-\dfrac{3}{2}\right)^{2}} =\sqrt{5^{2}+\left(\dfrac{5}{2}\right)^{2}} =\sqrt{25+\dfrac{25}{4}} =\sqrt{\dfrac{125}{4}} =\dfrac{\sqrt{125}}{2} =\dfrac{5\sqrt{5}}{2}.$$

Hence, the correct answer is Option B.

We are told that the ellipse is centred at the origin, and that one focus is at the point $$(0,\,5\sqrt{3})$$. Because this focus lies on the $$y$$-axis, the major axis must also be along the $$y$$-axis. Hence we may write the standard form of the ellipse as

$$\frac{x^{2}}{b^{2}}+\frac{y^{2}}{a^{2}}=1,$$

where $$a$$ is the semi-major axis, $$b$$ is the semi-minor axis and, by definition of “major”, we always have $$a \gt b$$.

For an ellipse in this orientation, the foci are located at $$(0,\pm c)$$, where the focal distance $$c$$ satisfies the well-known relation

$$c^{2}=a^{2}-b^{2}.$$

From the question, one of the foci is $$(0,5\sqrt{3})$$, so we immediately read off

$$c = 5\sqrt{3}.$$

Therefore, from the focal relation we have

$$a^{2}-b^{2}=c^{2}= \bigl(5\sqrt{3}\bigr)^{2}=25\cdot3=75.$$

Next, the question states that the difference of the lengths of the major and minor axes is $$10$$. The length of the major axis is $$2a$$ and that of the minor axis is $$2b$$, so

$$2a-2b=10 \quad\Longrightarrow\quad a-b=5.$$

We now possess the two equations

$$\begin{cases} a-b = 5,\\[4pt] a^{2}-b^{2} = 75. \end{cases}$$

Notice that $$a^{2}-b^{2}$$ factors conveniently:

$$a^{2}-b^{2}=(a-b)(a+b).$$

Substituting $$a-b=5$$ into this factorisation gives

$$5\,(a+b)=75 \quad\Longrightarrow\quad a+b = \frac{75}{5}=15.$$

We now have the simple linear system

$$\begin{cases} a-b = 5,\\ a+b = 15. \end{cases}$$

Adding the two equations:

$$2a = 20 \quad\Longrightarrow\quad a = 10.$$

Substituting $$a=10$$ into $$a-b=5$$ yields

$$10-b=5 \quad\Longrightarrow\quad b = 5.$$

With $$a=10$$ and $$b=5$$ found, we now compute the required length of the latus rectum. For an ellipse, the standard formula for the length $$L$$ of the latus rectum is

$$L = \frac{2b^{2}}{a}.$$

Substituting the values just obtained:

$$L = \frac{2\,(5)^{2}}{10}= \frac{2\cdot25}{10}= \frac{50}{10}=5.$$

Hence, the correct answer is Option D.

We are given the set

$$S=\Bigl\{(x,y)\in\mathbb R^{2}:\;\frac{y^{2}}{1+r}-\frac{x^{2}}{1-r}=1\Bigr\},\qquad r\ne\pm1.$$

First we inspect the signs of the denominators because the nature of the conic depends on them.

For $$r>1$$ we have $$1+r>0$$ and $$1-r<0.$$ To avoid the minus sign in the second fraction we rewrite it:

$$\frac{y^{2}}{1+r}-\frac{x^{2}}{1-r}=1 \;\Longrightarrow\; \frac{y^{2}}{1+r}+\frac{x^{2}}{r-1}=1,$$ because $$\frac{-x^{2}}{1-r}=\frac{x^{2}}{r-1}.$$

Now both denominators are positive, so the equation is of the form

$$\frac{y^{2}}{b^{2}}+\frac{x^{2}}{a^{2}}=1,$$

which is the standard equation of an ellipse. By simple comparison we have

$$a^{2}=r-1,\qquad b^{2}=1+r.$$ (Notice that because $$r>1,$$ we indeed have $$b^{2}>a^{2},$$ so the larger denominator has been kept with the $$y^{2}$$ term.)

For an ellipse, the eccentricity $$e$$ is defined by the relation

$$e=\frac{c}{b},\qquad\text{where }c^{2}=b^{2}-a^{2}.$$

We therefore calculate

$$c^{2}=b^{2}-a^{2}=(1+r)-(r-1)=2.$$

So

$$c=\sqrt{2}.$$

Substituting into the eccentricity formula we get

$$e=\frac{c}{b}=\frac{\sqrt{2}}{\sqrt{1+r}} =\sqrt{\frac{2}{1+r}}.$$

Thus, when $$r>1,$$ the curve is an ellipse whose eccentricity is $$\sqrt{\dfrac{2}{\,r+1\,}}.$$

This matches exactly the description in Option C.

For completeness, note that when $$0<r<1$$ both $$1+r$$ and $$1-r$$ are positive, so the original equation stays in the form

$$\frac{y^{2}}{1+r}-\frac{x^{2}}{1-r}=1,$$

which is the standard vertical hyperbola $$\dfrac{y^{2}}{a^{2}}-\dfrac{x^{2}}{b^{2}}=1.$$ One may show its eccentricity is $$\sqrt{\dfrac{2}{1+r}},$$ which is different from the values quoted in the other options, so none of the hyperbola statements is correct.

Hence, the correct answer is Option C.

We begin with the given ellipse

$$4x^{2}+y^{2}=8.$$

For a second-degree curve of the form $$Ax^{2}+By^{2}=C,$$ the equation of the tangent at a point $$(x_{1},y_{1})$$ lying on the curve is obtained by replacing each squared term by the product of the corresponding variables, namely

$$Axx_{1}+Byy_{1}=C.$$

Applying this directly to the ellipse (where $$A=4,\;B=1,\;C=8$$) we see that the tangent at any point $$(x_{1},y_{1})$$ on the ellipse is

$$4xx_{1}+yy_{1}=8.$$

One of the points is explicitly given as $$(1,\,2).$$ Substituting $$x_{1}=1,\;y_{1}=2$$ into the tangent formula gives

$$4x(1)+y(2)=8\;\Longrightarrow\;4x+2y=8.$$

Simplifying by dividing every term by $$2$$ we obtain

$$2x+y=4.$$

To read the slope, we write the line in the form $$y=mx+c:$$

$$y=-2x+4,$$

so the slope of this first tangent is

$$m_{1}=-2.$$

The problem states that the tangent at the unknown point $$(a,\,b)$$ is perpendicular to this one. The product of slopes of two perpendicular lines is $$-1,$$ that is,

$$m_{1}m_{2}=-1.$$

We already have $$m_{1}=-2,$$ so

$$(-2)\,m_{2}=-1\;\Longrightarrow\;m_{2}=\frac12.$$

Now we write the tangent at $$(a,\,b).$$ Using the same tangent formula, we first set up

$$4a\,x+b\,y=8.$$

To identify its slope, we solve for $$y$$:

$$b\,y=8-4a\,x,$$

so

$$y=\frac{8-4a\,x}{b}=-\frac{4a}{b}\,x+\frac{8}{b}.$$

Thus the slope of this second tangent is

$$m_{2}=-\frac{4a}{b}.$$

We already found that $$m_{2}=\dfrac12,$$ therefore

$$-\frac{4a}{b}=\frac12.$$

Cross-multiplying gives

$$2\!\left(-4a\right)=b,$$

or more simply

$$b=-8a.$$

The coordinates $$(a,\,b)$$ must also satisfy the original ellipse equation. Substituting $$b=-8a$$ into $$4a^{2}+b^{2}=8$$ we get

$$4a^{2}+(-8a)^{2}=8.$$

Expanding the squared term,

$$4a^{2}+64a^{2}=8,$$

which combines to

$$68a^{2}=8.$$

Solving for $$a^{2}$$ yields

$$a^{2}=\frac{8}{68}=\frac{4}{34}=\frac{2}{17}.$$

Hence, the correct answer is Option A.

We denote the semi-major axis by $$a$$, the semi-minor axis by $$b$$ and the eccentricity by $$e$$. For an ellipse whose major axis is the $$x$$-axis, the foci are $$S(ae,0)$$ and $$S'(-ae,0)$$, while the extremities of the minor axis are $$B(0,b)$$ and $$B'(0,-b)$$. In the problem we take $$B(0,b)$$.

First recall the two standard relations for an ellipse:

$$b^{2}=a^{2}(1-e^{2}) \qquad\text{and}\qquad \text{length of a latus rectum}= \dfrac{2b^{2}}{a}.$$

We are told that $$\triangle S'BS$$ is right-angled at $$B$$. The vectors $$\overrightarrow{BS}=(ae, -\,b)$$ and $$\overrightarrow{BS'}=(-ae, -\,b)$$ are therefore perpendicular, so their dot product must vanish:

$$\overrightarrow{BS}\cdot\overrightarrow{BS'} = (ae)(-ae)+(-b)(-b)= -\,a^{2}e^{2}+b^{2}=0.$$

Thus we obtain

$$b^{2}=a^{2}e^{2} \quad -(1).$$

Combining (1) with the basic ellipse relation $$b^{2}=a^{2}(1-e^{2})$$ we get

$$a^{2}e^{2}=a^{2}(1-e^{2}) \;\;\Longrightarrow\;\; e^{2}=1-e^{2} \;\;\Longrightarrow\;\; e^{2}=\dfrac12,$$

and hence

$$e=\dfrac1{\sqrt2}.$$

Next, we use the fact that the triangle is right-angled at $$B$$ and its area is $$8$$ sq. units. For a right triangle the area formula is

$$\text{Area}=\dfrac12(\text{product of the perpendicular sides}).$$

The perpendicular sides here are $$BS$$ and $$BS'$$, whose lengths are equal:

$$BS=\sqrt{(ae)^{2}+b^{2}}, \quad BS'=\sqrt{(-ae)^{2}+b^{2}}=\sqrt{(ae)^{2}+b^{2}}.$$

From (1) we have $$b^{2}=a^{2}e^{2}$$, so

$$BS=\sqrt{a^{2}e^{2}+a^{2}e^{2}}=\sqrt{2a^{2}e^{2}}=a e\sqrt2.$$

Since $$e=\dfrac1{\sqrt2}$$, this simplifies to

$$BS=a.$$

Now set up the area condition:

$$\dfrac12\,(BS)\,(BS')=\dfrac12\,a\,a=8 \;\;\Longrightarrow\;\; a^{2}=16 \;\;\Longrightarrow\;\; a=4.$$

With $$a=4$$, relation (1) gives

$$b^{2}=a^{2}e^{2}=16\left(\dfrac12\right)=8.$$

Finally, insert $$a=4$$ and $$b^{2}=8$$ into the latus rectum formula:

$$\text{latus rectum}= \dfrac{2b^{2}}{a}= \dfrac{2\times 8}{4}=4.$$

Hence, the correct answer is Option C.

We are given the ellipse $$3x^2 + 5y^2 = 32$$ and the point $$P(2,\,2)$$ on it. First we differentiate the equation of the ellipse implicitly to find the slope of the tangent. Differentiating, we obtain $$\frac{d}{dx}\,(3x^2) + \frac{d}{dx}\,(5y^2) = \frac{d}{dx}\,(32).$$

This gives $$6x + 10y\frac{dy}{dx} = 0.$$

So $$\frac{dy}{dx} = -\,\frac{6x}{10y} = -\,\frac{3x}{5y}.$$

At the point $$P(2,\,2)$$ we substitute $$x = 2,\; y = 2$$ to get the slope of the tangent:

$$m_{\text{tan}} = -\,\frac{3(2)}{5(2)} = -\,\frac{6}{10} = -\,\frac{3}{5}.$$

Now we write the tangent line in point-slope form $$y - y_1 = m(x - x_1).$$ Using $$P(2,\,2)$$ and $$m_{\text{tan}} = -\tfrac{3}{5},$$ we have

$$y - 2 = -\,\frac{3}{5}\,(x - 2).$$

To find point $$Q$$ where this tangent meets the x-axis, we set $$y = 0.$$ Substituting,

$$0 - 2 = -\,\frac{3}{5}\,(x_Q - 2).$$

Hence $$-2 = -\,\frac{3}{5}(x_Q - 2).$$

Multiplying both sides by $$-\frac{5}{3}$$, we get $$x_Q - 2 = \frac{10}{3},$$ so

$$x_Q = 2 + \frac{10}{3} = \frac{16}{3}.$$

Thus $$Q\Bigl(\frac{16}{3},\,0\Bigr).$$

Next, the slope of the normal is the negative reciprocal of the slope of the tangent. Since $$m_{\text{tan}} = -\frac{3}{5},$$ the normal slope is

$$m_{\text{norm}} = \frac{5}{3}.$$

Using the same point-slope form for the normal through $$P(2,\,2),$$ we write

$$y - 2 = \frac{5}{3}\,(x - 2).$$

To locate point $$R$$ where this normal meets the x-axis, we again set $$y = 0.$$ Substituting,

$$0 - 2 = \frac{5}{3}\,(x_R - 2).$$

This simplifies to $$-2 = \frac{5}{3}(x_R - 2).$$

Multiplying both sides by $$\frac{3}{5},$$ we obtain $$x_R - 2 = -\frac{6}{5},$$ hence

$$x_R = 2 - \frac{6}{5} = \frac{10}{5} - \frac{6}{5} = \frac{4}{5}.$$

Thus $$R\Bigl(\frac{4}{5},\,0\Bigr).$$

Now we have the three vertices of triangle $$PQR$$: $$P(2,\,2), \; Q\Bigl(\frac{16}{3},\,0\Bigr), \; R\Bigl(\frac{4}{5},\,0\Bigr).$$

Because $$Q$$ and $$R$$ lie on the x-axis, segment $$QR$$ is horizontal. Its length (the base of the triangle) is the absolute difference of their x-coordinates:

$$|\,x_Q - x_R| = \left|\,\frac{16}{3} - \frac{4}{5}\right|.$$

Using a common denominator $$15,$$ we have $$\frac{16}{3} = \frac{80}{15}, \qquad \frac{4}{5} = \frac{12}{15},$$ so

$$|\,x_Q - x_R| = \left|\frac{80}{15} - \frac{12}{15}\right| = \frac{68}{15}.$$

The height of the triangle is simply the y-coordinate of $$P,$$ which equals $$2.$$

The area formula for a triangle is $$\text{Area} = \tfrac12 \times (\text{base}) \times (\text{height}).$$ Substituting the base $$\frac{68}{15}$$ and the height $$2,$$ we obtain

$$\text{Area} = \frac12 \times \frac{68}{15} \times 2 = \frac{68}{15}.$$

Hence, the correct answer is Option A.