JEE Continuity & Differentiability Questions

First isolate the polynomial that encodes the condition “$$f(x)\neq g(x)$$ for every $$x$$”.
Define $$d(x)=f(x)-g(x)\,.$$

Using the given expressions,

$$\begin{aligned} d(x)&=\bigl(a_1+10x+a_2x^2+a_3x^3+x^4\bigr) -\bigl(b_1+3x+b_2x^2+b_3x^3+x^4\bigr)\\ &=\bigl(a_1-b_1\bigr)+\bigl(10-3\bigr)x+\bigl(a_2-b_2\bigr)x^2 +\bigl(a_3-b_3\bigr)x^3. \end{aligned}$$

The $$x^4$$ terms cancel, so $$d(x)$$ is at most cubic: $$d(x)=\alpha+\beta x+\gamma x^2+\delta x^3,$$ where $$\delta=a_3-b_3\,.$$

The statement $$f(x)\neq g(x)\;\forall x\in\mathbb{R}$$ means $$d(x)\neq 0$$ for all real $$x$$. If $$\delta\neq 0$$, then $$d(x)$$ is a genuine cubic. For a real cubic with non-zero leading coefficient,

$$\lim_{x\to\infty}d(x)=\text{sign}(\delta)\,\infty,\qquad \lim_{x\to-\infty}d(x)=-\text{sign}(\delta)\,\infty.$$

The Intermediate Value Theorem then forces at least one real root, contradicting $$d(x)\neq 0$$. Hence the cubic term must vanish:

$$\boxed{a_3-b_3=0}\;\Longrightarrow\;a_3=b_3.$$

Now compute the coefficient of $$x^3$$ in $$h(x)=f(x+1)-g(x+2).$$

First expand $$f(x+1)$$ and $$g(x+2)$$ up to the $$x^3$$ terms.

$$\begin{aligned} f(x+1)&=a_1+10(x+1)+a_2(x+1)^2+a_3(x+1)^3+(x+1)^4\\ &=\dots+\bigl(a_3+4\bigr)x^3+\dots\\[6pt] g(x+2)&=b_1+3(x+2)+b_2(x+2)^2+b_3(x+2)^3+(x+2)^4\\ &=\dots+\bigl(b_3+8\bigr)x^3+\dots \end{aligned}$$

(The intermediate “$$\dots$$” terms are not required because only the $$x^3$$ coefficients are needed.)

Subtract to get $$h(x)$$:

Coefficient of $$x^3$$ in $$h(x)$$ $$=\;(a_3+4)-(b_3+8)=a_3-b_3-4.$$

Using $$a_3=b_3$$ established above,

$$a_3-b_3-4=0-4=-4.$$

Therefore the coefficient of $$x^3$$ in $$h(x)$$ is $$\mathbf{-4}$$.

Option C which is: $$-4$$

The function is $$f(x) = (x^2+1)|x^2-ax+2| + \cos|x|$$. Note that $$\cos|x| = \cos x$$, which is differentiable everywhere, so any non-differentiability arises solely from the factor $$|x^2 - ax + 2|$$ and occurs where $$x^2 - ax + 2 = 0$$.

Since $$x = \alpha = 2$$ is given as a point of non-differentiability, it must satisfy $$4 - 2a + 2 = 0$$, which yields $$a = 3$$. Substituting this into the quadratic gives $$x^2 - 3x + 2 = (x-1)(x-2) = 0$$, so the roots are $$x = 1$$ and $$x = 2$$.

At $$x = 2$$, we have $$(x^2+1) = 5 \ne 0$$, confirming that the absolute value causes non-differentiability and hence $$\alpha = 2$$. At $$x = 1$$, we have $$(x^2+1) = 2 \ne 0$$, which similarly yields the other point of non-differentiability $$\beta = 1$$. Thus $$(\alpha,\beta) = (2,1)$$.

To find the distance from $$(2,1)$$ to the line $$12x + 5y + 10 = 0$$, we use the formula

$$ d = \frac{|12(2) + 5(1) + 10|}{\sqrt{144 + 25}} = \frac{|24 + 5 + 10|}{13} = \frac{39}{13} = 3 $$.

Therefore, the correct answer is Option 3: 3.

Case P: We need the smallest natural number $$n$$ such that the function $$f(x)=\left[\dfrac{10x^{3}-45x^{2}+60x+35}{n}\right]$$ is continuous on $$[1,2]$$.

The inner polynomial is $$p(x)=10x^{3}-45x^{2}+60x+35$$.
Evaluate at the end-points:

$$p(1)=10-45+60+35=60,\qquad p(2)=80-180+120+35=55.$$

Since $$p'(x)=30(x-1)(x-2)$$ is negative for $$1\lt x\lt 2,$$ $$p(x)$$ decreases strictly from $$60$$ to $$55$$, so on $$[1,2]$$ we have$$55\le p(x)\le 60.$$(The full range is actually $$[55,60]$$.)

Hence $$\dfrac{p(x)}{n}$$ lies in $$\left[\dfrac{55}{n},\dfrac{60}{n}\right]$$. For $$f(x)=[p(x)/n]$$ to be continuous, the entire interval $$[55/n,\,60/n]$$ must be contained in one open interval $$(k,k+1)$$ for some integer $$k$$ (otherwise the greatest-integer function jumps inside $$[1,2]$$).

The length of this interval is $$\dfrac{60-55}{n}=\dfrac{5}{n},$$ so we first need $$\dfrac{5}{n}\lt 1\;\Longrightarrow\;n\gt 5.$$ Now test successive natural numbers $$n\gt 5$$.

• $$n=6:\;[55/6,60/6]=[9.166\ldots,10].$$ The right end equals an integer; $$f(x)$$ jumps at $$x=1$$, so discontinuous.
• $$n=7:\;[7.857\ldots,8.571\ldots]$$ crosses the integer $$8$$ ⇒ discontinuous.
• $$n=8:\;[6.875,7.5]$$ crosses the integer $$7$$ ⇒ discontinuous.
• $$n=9:\;[6.111\ldots,6.666\ldots]\subset(6,7).$$ No integer is touched; hence $$f(x)$$ is continuous.

Thus the minimum $$n$$ is $$9$$. In List-II the number $$9$$ is entry (2). So (P) → (2).

Case Q: For $$g(x)=(2n^{2}-13n-15)(x^{3}+3x)$$ to be increasing on all $$\mathbb{R}$$ we need $$g'(x)\ge 0$$ everywhere.

$$g'(x)=(2n^{2}-13n-15)\bigl(3x^{2}+3\bigr)=3(2n^{2}-13n-15)(x^{2}+1).$$ Since $$x^{2}+1\gt 0$$ for all $$x,$$ the sign of $$g'(x)$$ is governed by $$A(n)=2n^{2}-13n-15.$$ Set $$A(n)\gt 0$$:

$$2n^{2}-13n-15\gt 0.$$

The roots of $$2n^{2}-13n-15=0$$ are $$n=\dfrac{13\pm\sqrt{169+120}}{4}=\dfrac{13\pm17}{4}\; \Rightarrow\; n=-1,\;7.5.$$ The quadratic is positive for $$n\gt 7.5$$ (or $$n\lt -1$$, which is irrelevant here). Hence the least natural $$n$$ making $$g$$ increasing is $$n=8$$.

Entry $$8$$ is (1) in List-II. So (Q) → (1).

Case R: We need the smallest natural $$n\gt 5$$ such that $$x=3$$ is a point of local minima of $$h(x)=(x^{2}-9)^{n}(x^{2}+2x+3).$$

Notice $$(x^{2}-9)^{n}=(x-3)^{n}(x+3)^{n},$$ and near $$x=3,$$ the factor $$(x+3)^{n}(x^{2}+2x+3)$$ is positive (its value at $$x=3$$ is $$6^{n}\cdot18\gt 0$$). Thus near $$x=3$$, $$h(x)$$ behaves like a positive constant times $$(x-3)^{n}$$.

• If $$n$$ is odd, $$(x-3)^{n}$$ changes sign about $$x=3$$, so $$x=3$$ is neither a local minimum nor a maximum.
• If $$n$$ is even, $$(x-3)^{n}\ge 0$$ with a zero at $$x=3$$ and positive values on both sides, giving a local minimum.

Therefore $$n$$ must be the smallest even natural number $$\gt 5,$$ i.e. $$n=6$$.

Entry $$6$$ is (4) in List-II. So (R) → (4).

Case S: Define $$l(x)=\sum_{k=0}^{4}\Bigl(\sin|x-k|+\cos\bigl|x-k+\tfrac12\bigr|\Bigr).$$ A finite sum is nondifferentiable exactly where at least one summand is nondifferentiable.

1. $$\sin|t|$$ is nondifferentiable at $$t=0$$ because $$\dfrac{d}{dt}\sin|t|=\cos|t|\operatorname{sgn}(t),$$ whose one-sided limits at $$t=0$$ are $$+1$$ and $$-1$$.

2. $$\cos|t|$$ is differentiable everywhere since $$\dfrac{d}{dt}\cos|t|=-\sin|t|\operatorname{sgn}(t),$$ and both one-sided limits at $$t=0$$ are $$0$$.

Hence nondifferentiability of $$l(x)$$ occurs only where $$|x-k|=0$$, i.e. at $$x=k,\quad k=0,1,2,3,4.$$ (The cos-terms never introduce new singularities.)

Thus there are $$5$$ real numbers $$x_{0}$$ at which $$l(x)$$ is not differentiable.

Entry $$5$$ in List-II corresponds to the number $$5$$. So (S) → (3).

Collecting all the matches:
(P) → (2), (Q) → (1), (R) → (4), (S) → (3).

Therefore the correct option is:
Option B which is: (P)→(2), (Q)→(1), (R)→(4), (S)→(3).

The function is defined as

$$f(x)=\begin{cases}(1+ax)^{1/x}, & x\lt 0\\[4pt]1+b, & x=0\\[4pt]\dfrac{(x+4)^{1/2}-2}{(x+c)^{1/3}-2}, & x\gt 0\end{cases}$$

For continuity at $$x=0$$ we must have

$$\lim_{x\to 0^-}f(x)=f(0)=\lim_{x\to 0^+}f(x).$$

Case 1 : Left-hand limit

Recall the standard limit $$\lim_{x\to 0}\left(1+kx\right)^{\tfrac{1}{x}}=e^{k}.$$ Putting $$k=a$$, we get

$$\lim_{x\to 0^-}(1+ax)^{1/x}=e^{a}.$$

Case 2 : Value at $$x=0$$

From the definition, $$f(0)=1+b.$$ Continuity demands

$$e^{a}=1+b \quad -(1)$$

Case 3 : Right-hand limit

We first make the denominator zero at $$x=0$$ so that a finite limit can exist:

$$\bigl(x+c\bigr)^{1/3}-2=0\ \text{ at }x=0\;\Rightarrow\;c^{1/3}=2\;\Rightarrow\;c=8.$$

Now evaluate the limit with $$c=8$$:

$$L=\lim_{x\to 0^+}\dfrac{(x+4)^{1/2}-2}{(x+8)^{1/3}-2}.$$

Let $$x\to 0^+$$, write $$x=h$$ with $$h\to 0^+$$.

Numerator expansion around $$h=0$$: $$(4+h)^{1/2}=2\left(1+\tfrac{h}{4}\right)^{1/2}\approx 2\left(1+\tfrac{1}{2}\cdot\tfrac{h}{4}\right)=2+\tfrac{h}{4}.$$ Hence $$(4+h)^{1/2}-2\approx\tfrac{h}{4}.$$

Denominator expansion around $$h=0$$: $$(8+h)^{1/3}=2\left(1+\tfrac{h}{8}\right)^{1/3}\approx2\left(1+\tfrac{1}{3}\cdot\tfrac{h}{8}\right)=2+\tfrac{h}{12}.$$ Hence $$(8+h)^{1/3}-2\approx\tfrac{h}{12}.$$

Therefore

$$L=\lim_{h\to 0^+}\dfrac{\tfrac{h}{4}}{\tfrac{h}{12}}=\dfrac{1/4}{1/12}=3.$$

Continuity requires this limit to equal $$f(0)=1+b$$, so

$$1+b=3\;\Rightarrow\;b=2 \quad -(2)$$

Using $$(1)$$ and $$(2)$$:

$$e^{a}=1+b=3\;\Rightarrow\;a=\ln 3.$$

We already obtained $$c=8$$. Finally, compute $$e^{a}\,b\,c$$:

$$e^{a}\,b\,c = 3 \times 2 \times 8 = 48.$$

Thus $$e^{a}bc = 48$$, which corresponds to Option C.

We have to evaluate the limit
$$\lim_{x \to 0}\; \frac{\tan(\tan x)\;-\;\sin(\sin x)}{\tan x\;-\;\sin x}$$
because, for continuity at $$x = 0$$, the value $$f(0)$$ must equal this limit.

Step 1: Expand $$\tan x$$ and $$\sin x$$ about $$x = 0$$ up to the order $$x^{3}$$.
$$\tan x = x + \frac{x^{3}}{3} + O(x^{5})$$
$$\sin x = x - \frac{x^{3}}{6} + O(x^{5})$$

Step 2: Denote
$$A = \tan x, \qquad B = \sin x.$$
Using the results from Step 1,
$$A - B = \left(x + \frac{x^{3}}{3}\right) - \left(x - \frac{x^{3}}{6}\right) + O(x^{5}) = \frac{x^{3}}{2} + O(x^{5}).$$

Step 3: Expand $$\tan A$$ and $$\sin B$$ for small arguments $$A, B$$.
For any small $$y$$,
$$\tan y = y + \frac{y^{3}}{3} + O(y^{5}),$$
$$\sin y = y - \frac{y^{3}}{6} + O(y^{5}).$$
Applying these with $$y = A$$ and $$y = B$$:

$$\tan(\tan x) = \tan A = A + \frac{A^{3}}{3} + O(x^{5}),$$
$$\sin(\sin x) = \sin B = B - \frac{B^{3}}{6} + O(x^{5}).$$

Step 4: Form the numerator.
$$\tan A - \sin B = (A - B) + \left(\frac{A^{3}}{3} + \frac{B^{3}}{6}\right) + O(x^{5}).$$

Because $$A = x + O(x^{3})$$ and $$B = x + O(x^{3})$$, we have $$A^{3} = x^{3} + O(x^{5})$$ and $$B^{3} = x^{3} + O(x^{5}).$$ Hence
$$\frac{A^{3}}{3} + \frac{B^{3}}{6} = \frac{x^{3}}{3} + \frac{x^{3}}{6} + O(x^{5}) = \frac{x^{3}}{2} + O(x^{5}).$$

Therefore
$$\tan A - \sin B = \left(\frac{x^{3}}{2}\right) + \left(\frac{x^{3}}{2}\right) + O(x^{5}) = x^{3} + O(x^{5}).$$

Step 5: Form the denominator (already obtained in Step 2):
$$\tan x - \sin x = \frac{x^{3}}{2} + O(x^{5}).$$

Step 6: Take the ratio and pass to the limit:
$$\frac{\tan(\tan x) - \sin(\sin x)}{\tan x - \sin x} = \frac{x^{3} + O(x^{5})}{\dfrac{x^{3}}{2} + O(x^{5})} = \frac{x^{3}\left[1 + O(x^{2})\right]}{\dfrac{x^{3}}{2}\left[1 + O(x^{2})\right]} = 2 \cdot \frac{1 + O(x^{2})}{1 + O(x^{2})}.$$

As $$x \to 0$$, the terms $$O(x^{2})$$ vanish, giving
$$\lim_{x \to 0}\; \frac{\tan(\tan x) - \sin(\sin x)}{\tan x - \sin x} = 2.$$

Hence, to make $$f(x)$$ continuous at $$x = 0$$, we must define
$$f(0) = 2.$$

Answer: $$f(0) = 2$$.

$$f(x)$$ on $$[0, 2]$$ is $$\min\{1+x+[x], x+2[x]\}$$.

• $$0 \leq x < 1$$: $$\min\{1+x, x\} = x$$

• $$1 \leq x < 2$$: $$\min\{2+x, x+2\} = x+2$$

• At $$x=2$$: $$\min\{1+2+2, 2+4\} = 5$$

Full function:

$$f(x) = \begin{cases} 3x & x < 0 \\ x & 0 \leq x < 1 \\ x+2 & 1 \leq x < 2 \\ 5 & x \geq 2 \end{cases}$$

• Continuity $$(\alpha)$$:

o At $$x=0$$: $$LHL=0, RHL=0$$ (Cont.)

o At $$x=1$$: $$LHL=1, RHL=3$$ (Discont.)

o At $$x=2$$: $$LHL=4, RHL=5$$ (Discont.)

$$\alpha = 2$$

• Differentiability $$(\beta)$$:

o Not diff at $$x=1, 2$$ (due to discontinuity).

o At $$x=0$$: $$LHD=3, RHD=1$$ (Not diff.)

$$\beta = 3$$

Total $$\alpha + \beta = 2 + 3 = \mathbf{5}$$.

We are given the differential equation $$f''(x)=f(x)$$ together with the facts that $$f$$ is thrice differentiable, odd, $$f'(x)\ge 0$$ for all $$x$$, $$f(0)=0$$ and $$f'(0)=3$$. Our goal is to find $$9f(\log_e 3)$$.

Step 1 - General solution of $$f''(x)=f(x)$$.
For the linear, constant-coefficient differential equation $$f''(x)=f(x)$$, the auxiliary equation is $$m^2-1=0$$ giving roots $$m=\pm1$$. Hence the general solution is
$$f(x)=C_1e^{x}+C_2e^{-x}$$ $$-(1)$$

Step 2 - Using the odd-function condition.
Because $$f$$ is odd, $$f(-x)=-f(x)$$ for every $$x$$. Substitute $$-x$$ in $$(1)$$:
$$f(-x)=C_1e^{-x}+C_2e^{x}$$.
Set this equal to $$-f(x)=-(C_1e^{x}+C_2e^{-x})$$:
$$C_1e^{-x}+C_2e^{x}= -C_1e^{x}-C_2e^{-x}$$.
Collecting like terms gives$$(C_1+C_2)(e^{x}+e^{-x})=0 \quad\text{for all }x.$$
Since $$e^{x}+e^{-x}\neq0$$, we must have $$C_1+C_2=0$$, so $$C_2=-C_1$$.

Step 3 - Rewrite $$f(x)$$ with a single constant.
Insert $$C_2=-C_1$$ in $$(1)$$:
$$f(x)=C_1(e^{x}-e^{-x})=2C_1\sinh x.$$
Let $$k=2C_1$$; then
$$f(x)=k\sinh x.$$ $$-(2)$$

Step 4 - Use the initial slope $$f'(0)=3$$.
Differentiate $$(2)$$:
$$f'(x)=k\cosh x.$$
At $$x=0$$, $$\cosh 0=1$$, so
$$f'(0)=k\cdot1=3\quad\Longrightarrow\quad k=3.$$

Step 5 - Explicit form of $$f(x)$$.
With $$k=3$$, equation $$(2)$$ becomes
$$f(x)=3\sinh x.$$
Notice $$f'(x)=3\cosh x\ge0$$ for all $$x$$, satisfying the given monotonicity condition.

Step 6 - Evaluate $$f(\log_e 3)$$.
Let $$u=\log_e 3$$, then $$e^{u}=3$$ and $$e^{-u}=1/3$$.
Recall $$\sinh u=\dfrac{e^{u}-e^{-u}}{2}$$, so
$$\sinh(\log_e 3)=\frac{3-\frac13}{2}=\frac{9-1}{6}=\frac83=\frac43.$$
Therefore
$$f(\log_e 3)=3\left(\frac43\right)=4.$$

Step 7 - Compute $$9f(\log_e 3)$$.
$$9f(\log_e 3)=9\times4=36.$$

Hence the required value is $$36$$.

The function is the maximum of all odd powers of $$x$$ up to $$x^{21}$$:
$$f(x)=\max\{x,\;x^{3},\;x^{5},\ldots ,x^{21}\},\qquad x\in\mathbb{R}$$

Because all exponents are odd, the sign of every term equals the sign of $$x$$. To decide which power is largest in each interval, compare their magnitudes.

Case 1: $$x\gt 1$$.
For numbers bigger than $$1$$, the higher the exponent, the larger the value. Hence the $$21^{\text{st}}$$ power dominates:
$$f(x)=x^{21},\qquad x\in(1,\infty)$$

Case 2: $$0\lt x\lt 1$$.
For numbers between $$0$$ and $$1$$, higher exponents make the value smaller. Thus the first power is the greatest:
$$f(x)=x,\qquad x\in(0,1)$$

Case 3: $$-1\lt x\lt 0$$.
Here the values are negative but their absolute values are less than $$1$$. The term closest to zero (largest among negatives) is again the highest exponent:
$$f(x)=x^{21},\qquad x\in(-1,0)$$

Case 4: $$x\lt -1$$.
For negative numbers with magnitude exceeding $$1$$, higher powers are more negative. The least negative term is the first power:
$$f(x)=x,\qquad x\in(-\infty,-1)$$

The only points where the defining formula changes are $$x=-1,\,0,\,1$$. These are the only candidates for non-continuity or non-differentiability.

Continuity check

Compute the two candidate expressions at the switching points.

At $$x=-1$$: $$x=-1,\;x^{21}=(-1)^{21}=-1\;\Rightarrow\;f(-1)=-1$$.
Both one-sided limits equal $$-1$$, so $$f$$ is continuous.

At $$x=0$$: all terms are $$0\;\Rightarrow\;f(0)=0$$. Both one-sided limits are $$0$$, so $$f$$ is continuous.

At $$x=1$$: $$x=1,\;x^{21}=1\;\Rightarrow\;f(1)=1$$. Both one-sided limits are $$1$$, so $$f$$ is continuous.

Therefore the function is continuous everywhere, giving
$$n=0$$

Differentiability check

On each open interval the function equals an elementary power and is differentiable. Check derivatives from the left and right at the three boundary points.

The two relevant derivatives are
Left region (where $$f(x)=x$$): $$f'(x)=1$$.
Right region (where $$f(x)=x^{21}$$): $$f'(x)=21x^{20}$$.

• At $$x=-1$$: left derivative $$1$$, right derivative $$21(-1)^{20}=21$$ ⟹ unequal.
• At $$x=0$$: left derivative $$21(0)^{20}=0$$, right derivative $$1$$ ⟹ unequal.
• At $$x=1$$: left derivative $$1$$, right derivative $$21(1)^{20}=21$$ ⟹ unequal.

Hence $$f(x)$$ is not differentiable at exactly three points: $$x=-1,\,0,\,1$$.
Thus
$$m=3$$

Finally, $$m+n=3+0=3$$.

Answer: 3

The function is defined by
$$f(x)=\begin{cases}2-2x^{2}-x^{2}\sin\frac1x,&x\neq0\\[4pt]2,&x=0\end{cases}$$

1. Continuity at $$x=0$$
$$\displaystyle\lim_{x\to0}\bigl(2-2x^{2}-x^{2}\sin\tfrac1x\bigr)=2-0-0=2=f(0)$$
Hence $$f$$ is continuous at the origin.

2. Differentiability at $$x=0$$
Use the definition of the derivative:

$$\begin{aligned} f'(0)&=\lim_{h\to0}\frac{f(h)-f(0)}{h} =\lim_{h\to0}\frac{-2h^{2}-h^{2}\sin\tfrac1h}{h}\\[4pt] &=\lim_{h\to0}\bigl(-h(2+\sin\tfrac1h)\bigr)=0. \end{aligned}$$
The limit exists, so $$f$$ is differentiable at $$x=0$$ with $$f'(0)=0$$. Therefore Option A is false.

3. Derivative for $$x\neq0$$
Differentiate term-wise:

$$\begin{aligned} f'(x)&=\frac{d}{dx}\Bigl(-2x^{2}-x^{2}\sin\tfrac1x\Bigr)\\[4pt] &=-4x-\Bigl[2x\sin\tfrac1x-x^{2}\cos\tfrac1x\cdot\frac1{x^{2}}\Bigr]\\[4pt] &=-4x-2x\sin\tfrac1x+\cos\tfrac1x\\[4pt] &=\cos\tfrac1x-4x-2x\sin\tfrac1x.\qquad(x\neq0) \end{aligned}$$

Near the origin the terms $$-4x$$ and $$-2x\sin\tfrac1x$$ are of order $$x$$ and tend to $$0$$, while $$\cos\tfrac1x$$ oscillates between $$-1$$ and $$1$$. Hence the sign of $$f'(x)$$ changes infinitely often in every punctured neighbourhood of $$0$$.

4. Testing the options

Option B: To be decreasing on $$(0,\delta)$$ we would need $$f'(x)\le0$$ for all $$x\in(0,\delta)$$. But pick a sequence $$x_n=\tfrac1{2n\pi}$$; then $$\cos\tfrac1{x_n}=\cos(2n\pi)=1$$ and

$$f'(x_n)=1-4x_n-2x_n\sin(2n\pi)=1-4x_n>0$$

for all sufficiently large $$n$$. Thus $$f$$ is not always decreasing on any interval $$(0,\delta)$$, so Option B is false.

Option C: To be increasing on $$(-\delta,0)$$ we would need $$f'(x)\ge0$$ there. Take the sequence $$y_n=-\tfrac1{(2n+1)\pi}$$; then $$\cos\tfrac1{y_n}=\cos\bigl(-(2n+1)\pi\bigr)=-1$$ and

$$f'(y_n)=-1-4y_n-2y_n\sin\bigl(-(2n+1)\pi\bigr)=-1-4y_n<0$$

for all large $$n$$ (since $$y_n\to0^-$$). Therefore, no matter how small $$\delta$$ is chosen, $$f'(x)$$ takes negative values in $$(-\delta,0)$$, so $$f$$ cannot be increasing there. Hence Option C is true.

Option D: For $$x\neq0$$ we have
$$f(x)=2-x^{2}\bigl(2+\sin\tfrac1x\bigr), \qquad 1\le2+\sin\tfrac1x\le3,$$
so $$f(x)\le2-x^{2}<2$$ for every non-zero $$x$$. Thus $$f(0)=2$$ is a strict maximum, not a minimum. Therefore Option D is false.

Conclusion
The only correct statement is Option C: “For any positive real number $$\delta$$, the function $$f$$ is NOT an increasing function on the interval $$(-\delta,0)$$.”

We are given that $$(\sin x \cos y)(f(2x+2y) - f(2x-2y)) = (\cos x \sin y)(f(2x+2y) + f(2x-2y))$$ for all $$x, y \in \mathbb{R}$$.

Rearranging: $$\sin x \cos y \cdot f(2x+2y) - \sin x \cos y \cdot f(2x-2y) = \cos x \sin y \cdot f(2x+2y) + \cos x \sin y \cdot f(2x-2y)$$.

Collecting terms with $$f(2x+2y)$$ and $$f(2x-2y)$$:

$$f(2x+2y)(\sin x \cos y - \cos x \sin y) = f(2x-2y)(\sin x \cos y + \cos x \sin y)$$

Using the sine addition and subtraction formulas: $$\sin x \cos y - \cos x \sin y = \sin(x-y)$$ and $$\sin x \cos y + \cos x \sin y = \sin(x+y)$$.

So $$f(2x+2y) \sin(x-y) = f(2x-2y) \sin(x+y)$$.

This gives $$\frac{f(2x+2y)}{\sin(x+y)} = \frac{f(2x-2y)}{\sin(x-y)}$$.

Let $$u = x+y$$ and $$v = x-y$$. Then $$\frac{f(2u)}{\sin u} = \frac{f(2v)}{\sin v}$$ for all valid $$u, v$$. This means $$\frac{f(2u)}{\sin u}$$ is a constant, say $$c$$.

Therefore $$f(t) = c \sin\left(\frac{t}{2}\right)$$ for all $$t$$.

Now $$f'(t) = \frac{c}{2} \cos\left(\frac{t}{2}\right)$$. Given $$f'(0) = \frac{1}{2}$$:

$$\frac{c}{2} \cos(0) = \frac{1}{2}$$, so $$\frac{c}{2} = \frac{1}{2}$$, giving $$c = 1$$.

Therefore $$f(t) = \sin\left(\frac{t}{2}\right)$$, $$f'(t) = \frac{1}{2}\cos\left(\frac{t}{2}\right)$$, and $$f''(t) = -\frac{1}{4}\sin\left(\frac{t}{2}\right)$$.

Now $$f''\left(\frac{5\pi}{3}\right) = -\frac{1}{4}\sin\left(\frac{5\pi}{6}\right) = -\frac{1}{4} \cdot \frac{1}{2} = -\frac{1}{8}$$.

Therefore $$24 f''\left(\frac{5\pi}{3}\right) = 24 \cdot \left(-\frac{1}{8}\right) = -3$$.

Hence, the correct answer is Option B.

For continuity, $$LHL = RHL = f(0) = 4$$.

1. Left Hand Limit (LHL):

$$\lim_{x \to 0^-} \frac{2}{x} (\sin((k_1+1)x) + \sin((k_2-1)x))$$

Using $$\lim_{x \to 0} \frac{\sin ax}{x} = a$$:

$$LHL = 2((k_1+1) + (k_2-1)) = 2(k_1 + k_2)$$.

Set $$2(k_1 + k_2) = 4 \implies \mathbf{k_1 + k_2 = 2}$$.

2. Right Hand Limit (RHL):

$$\lim_{x \to 0^+} \frac{2}{x} \log_e \left( \frac{2+k_1x}{2+k_2x} \right) = \lim_{x \to 0^+} \frac{2}{x} \log_e \left( \frac{1+\frac{k_1}{2}x}{1+\frac{k_2}{2}x} \right)$$

Using $$\lim_{x \to 0} \frac{\log(1+ax)}{x} = a$$:

$$RHL = 2(\frac{k_1}{2} - \frac{k_2}{2}) = k_1 - k_2$$.

Set $$k_1 - k_2 = 4$$.

Solving for $$k_1, k_2$$:

Adding the equations: $$2k_1 = 6 \implies k_1 = 3$$.

Subtracting: $$2k_2 = -2 \implies k_2 = -1$$.

Result: $$k_1^2 + k_2^2 = 3^2 + (-1)^2 = 9 + 1 = \mathbf{10}$$. (Option D

The function is given by
$$f(x)=\dfrac{6x+\sin x}{2x+\sin x}\;,\;x\neq 0,\qquad f(0)=\dfrac73.$$

1. Behaviour at the origin

First-order Taylor expansion about $$x=0$$ gives

$$\sin x=x-\dfrac{x^{3}}6+O(x^{5}),\qquad \cos x=1-\dfrac{x^{2}}2+O(x^{4}).$$

Hence

$$6x+\sin x=6x+\left(x-\dfrac{x^{3}}6\right)=7x-\dfrac{x^{3}}6+O(x^{5}),$$ $$2x+\sin x=2x+\left(x-\dfrac{x^{3}}6\right)=3x-\dfrac{x^{3}}6+O(x^{5}).$$

Therefore

$$f(x)=\dfrac{7x-\dfrac{x^{3}}6+O(x^{5})}{3x-\dfrac{x^{3}}6+O(x^{5})} =\dfrac73\!\left[\,1+\dfrac{2x^{2}}{63}+O(x^{4})\right] =\dfrac73+\dfrac{2x^{2}}{27}+O(x^{4}).$$

Near the origin we thus have

$$f(x)=\dfrac73+\dfrac{2x^{2}}{27}+O(x^{4}).$$

This gives $$f'(0)=0$$ and $$f''(0)=\dfrac{4}{27}\;(\gt 0).$$ Hence $$x=0$$ is a point of local minimum. Option B is therefore correct, while Option A is not.

2. Critical points for $$x\neq 0$$

For $$x\neq 0$$ write $$N=6x+\sin x,\;D=2x+\sin x,$$ so that $$f(x)=\dfrac{N}{D}.$$ Using the quotient rule,

$$f'(x)=\dfrac{N' D-N D'}{D^{2}} =\dfrac{(6+\cos x)(2x+\sin x)-(6x+\sin x)(2+\cos x)}{(2x+\sin x)^{2}} =\dfrac{4\bigl(\sin x-x\cos x\bigr)}{(2x+\sin x)^{2}}.$$

Since $$(2x+\sin x)^{2}\gt 0\quad\text{for all }x\gt 0,$$ the sign of $$f'(x)$$ is governed solely by

$$g(x)=\sin x-x\cos x.$$

3. Location of critical points

Setting $$f'(x)=0$$ gives $$g(x)=0\iff \sin x-x\cos x=0 \iff\tan x = x.$$ The well-known equation $$\tan x=x$$ has one solution in every interval $$\bigl(n\pi,\;n\pi+\tfrac{\pi}{2}\bigr), \;n=1,2,3,\ldots$$ apart from $$x=0.$$ Denote these positive roots by $$x_1,x_2,x_3,\dots$$ in increasing order:

$$x_1\approx4.493,\;x_2\approx7.725,\;x_3\approx10.904,\; x_4\approx14.066,\;x_5\approx17.279,\;\ldots$$

4. Nature of each critical point

Differentiate $$g(x)$$:

$$g'(x)=\cos x-\cos x+x\sin x = x\sin x.$$

Thus, at a root $$x_n,$$ the sign of $$g'(x_n)=x_n\sin x_n$$ is the sign of $$\sin x_n.$$ Inside $$\bigl(n\pi,\;n\pi+\tfrac{\pi}{2}\bigr)$$ we have $$\sin x\;\begin{cases} \gt 0,& n\; \text{even},\\[4pt] \lt 0,& n\; \text{odd}. \end{cases}$$ Therefore

• If $$n$$ is odd ($$1,3,5,\dots$$) then $$g'(x_n)\lt 0:$$ $$g(x)$$ crosses the $$x$$-axis from positive to negative, so $$f'(x)$$ changes $$+\to-$$ and $$x_n$$ is a local maximum.
• If $$n$$ is even ($$2,4,6,\dots$$) then $$g'(x_n)\gt 0:$$ $$g(x)$$ crosses from negative to positive, so $$f'(x)$$ changes $$-\to+$$ and $$x_n$$ is a local minimum.

5. Counting extrema in the required intervals

(i) Interval $$[\pi,6\pi]\;( \approx[3.142,18.850] ):$$ roots inside this range are $$x_1,x_2,x_3,x_4,x_5.$$ Among these, maxima occur at the odd-indexed roots $$x_1,x_3,x_5.$$ Hence the number of local maxima is $$3.$$ Option C is correct.

(ii) Interval $$[2\pi,4\pi]\;( \approx[6.283,12.566] ):$$ only the root $$x_2\approx7.725$$ lies in this interval, and it is a local minimum (even index). Therefore there is exactly $$1$$ local minimum here. Option D is correct.

6. Final verdict

The true statements are:
Option B, Option C, and Option D.

 $$|x - 2|$$ is continuous everywhere and $$[x]$$ is discontinuous at all integers, within the interval $$(-2,3)$$ the integers are $$-1, 0, 1, 2$$.

Because $$f(x)$$ combines these two parts and only $$[x]$$ causes discontinuities, it follows that $$f(x)$$ is discontinuous exactly at $$x = -1, 0, 1, 2$$, giving $$m = 4$$.

 $$x = -1, 0, 1, 2$$, $$f$$ is non-differentiable at those four points. Although $$|x - 2|$$ introduces a corner at $$x = 2$$, this point has already been counted among the discontinuities. No additional points of non-differentiability arise because between consecutive integers both $$[x]$$ (which is constant) and $$|x - 2|$$ (which is linear) are differentiable. Therefore, $$n = 4$$.

$$m + n = 4 + 4 = 8$$.

The four basic building blocks are

$$f(x)=\begin{cases}x|x|\sin\!\left(\dfrac1x\right),&x\neq0\\[4pt]0,&x=0\end{cases},\qquad g(x)=\begin{cases}1-2x,&0\le x\le\dfrac12\\[4pt]0,&\text{otherwise}\end{cases}$$

and the composite function

$$h(x)=a\,f(x)+b\,[\,g(x)+g\!\left(\tfrac12-x\right)]+c\,[\,x-g(x)]+d\,g(x).$$

Case P (a=0, b=1, c=0, d=0)

Then $$h(x)=g(x)+g\!\left(\tfrac12-x\right).$$
For $$0\le x\le\dfrac12$$ we have $$g(x)=1-2x$$ and, since $$0\le\dfrac12-x\le\dfrac12,$$

$$g\!\left(\tfrac12-x\right)=1-2\!\left(\tfrac12-x\right)=2x.$$

Hence $$h(x)=1-2x+2x=1\quad\text{for }0\le x\le\dfrac12.$$

For $$x\lt0$$ or $$x\gt\dfrac12$$ both arguments of $$g$$ lie outside $$[0,\tfrac12],$$ so $$g=0$$ there and $$h(x)=0.$$ Thus $$h(x)=\begin{cases}1,&0\le x\le\dfrac12\\[4pt]0,&\text{otherwise}\end{cases}.$$

The only attained values are $$0$$ and $$1,$$ so the range is $$\{0,1\}.$$ This matches item (5).

Case Q (a=1, b=0, c=0, d=0)

Here $$h(x)=f(x)=x|x|\sin\!\left(\dfrac1x\right)\;(x\ne0),\;h(0)=0.$$

Differentiability at $$x=0$$:

$$\lim_{h\to0}\dfrac{f(h)-f(0)}h =\lim_{h\to0}|h|\sin\!\left(\dfrac1h\right)=0,$$ because $$|\,\sin(1/h)\,|\le1$$ and $$|h|\to0.$$
For $$x\ne0$$ the formula is a product/composition of differentiable functions, so $$f$$ is differentiable there as well. Hence $$h$$ is differentiable on the whole of $$\mathbb R,$$ giving item (3).

Case R (a=0, b=0, c=1, d=0)

Now $$h(x)=x-g(x).$$ Using the definition of $$g$$:

$$h(x)=\begin{cases} x,&x\lt0\\[4pt] x-(1-2x)=3x-1,&0\le x\le\dfrac12\\[4pt] x,&x\gt\dfrac12 \end{cases}$$

Ranges of the three pieces:

• $$x\lt0:\;h=x\;\Longrightarrow\;(-\infty,0)$$
• $$0\le x\le\dfrac12:\;h=3x-1\;\Longrightarrow\;[-1,\tfrac12]$$
• $$x\gt\dfrac12:\;h=x\;\Longrightarrow\;(\tfrac12,\infty)$$

The union $$(-\infty,0)\cup[-1,\tfrac12]\cup(\tfrac12,\infty)=\mathbb R.$$ Therefore every real number is achieved; $$h$$ is onto, corresponding to item (2).

Case S (a=0, b=0, c=0, d=1)

Then $$h(x)=g(x).$$ For $$0\le x\le\dfrac12,\;h(x)=1-2x,$$ which decreases continuously from $$1$$ to $$0.$$ Hence $$\operatorname{Range}(h)=[0,1],$$ giving item (4).

Collecting all the matches:

P → (5), Q → (3), R → (2), S → (4).

Thus the correct option is
Option C which is: (P) → (5), (Q) → (3), (R) → (2), (S) → (4).

The given function is

$$f(x)=\begin{cases}x^{2}\sin\!\left(\dfrac{\pi}{x^{2}}\right), & x\ne 0,\\[4pt] 0, & x=0.\end{cases}$$

For $$x\ne 0$$ the factor $$x^{2}$$ is never zero, so the zeros of $$f(x)$$ (apart from $$x=0$$) come only from the sine term:

$$\sin\!\left(\dfrac{\pi}{x^{2}}\right)=0 \;\Longrightarrow\; \dfrac{\pi}{x^{2}}=n\pi,\; n\in\mathbb{Z}.$$ Cancelling $$\pi$$ (and discarding $$n=0$$ because it would give the undefined value $$x=\infty$$) we get

$$\dfrac{1}{x^{2}}=n,\; n=1,2,3,\dots$$ $$\Longrightarrow\; x=\pm\dfrac{1}{\sqrt{n}}.$$

Therefore, for positive $$x$$ the zeros are exactly

$$x_{n}=\dfrac{1}{\sqrt{n}},\quad n=1,2,3,\dots$$

We now test each option.

Option A: $$f(x)=0$$ has infinitely many solutions in $$\Bigl[\dfrac{1}{10^{10}},\infty\Bigr).$$
The condition $$x_{n}\ge\dfrac{1}{10^{10}}$$ gives $$\dfrac{1}{\sqrt{n}}\ge\dfrac{1}{10^{10}} \;\Longrightarrow\; \sqrt{n}\le 10^{10} \;\Longrightarrow\; n\le 10^{20}.$$ There are only $$10^{20}$$ such integers, a (very) large but finite number. Hence Option A is false.

Option B: $$f(x)=0$$ has no solutions in $$\Bigl[\dfrac{1}{\pi},\infty\Bigr).$$
Require $$x_{n}\ge\dfrac{1}{\pi} \;\Longrightarrow\; \dfrac{1}{\sqrt{n}}\ge\dfrac{1}{\pi} \;\Longrightarrow\; \sqrt{n}\le\pi \;\Longrightarrow\; n\le\pi^{2}\approx 9.87.$$ The integers $$n=1,2,\dots,9$$ all satisfy this, so there are nine zeros in the stated interval. Hence Option B is false.

Option C: The set of solutions of $$f(x)=0$$ in $$\Bigl(0,\dfrac{1}{10^{10}}\Bigr)$$ is finite.
Here we need $$x_{n}\lt\dfrac{1}{10^{10}} \;\Longrightarrow\; \dfrac{1}{\sqrt{n}}\lt\dfrac{1}{10^{10}} \;\Longrightarrow\; \sqrt{n}\gt 10^{10} \;\Longrightarrow\; n\gt 10^{20}.$$ All integers $$n=10^{20}+1,10^{20}+2,\dots$$ work, and there are infinitely many of them. So Option C is false.

Option D: $$f(x)=0$$ has more than 25 solutions in $$\Bigl(\dfrac{1}{\pi^{2}},\dfrac{1}{\pi}\Bigr).$$
The inequalities $$\dfrac{1}{\pi^{2}}\lt x_{n}\lt\dfrac{1}{\pi}$$ give $$\dfrac{1}{\pi^{2}}\lt\dfrac{1}{\sqrt{n}}\lt\dfrac{1}{\pi} \;\Longrightarrow\; \pi\lt\sqrt{n}\lt\pi^{2} \;\Longrightarrow\; \pi^{2}\lt n\lt\pi^{4}.$$ Numerically, $$\pi^{2}\approx 9.87,\qquad \pi^{4}\approx 97.41.$$ Thus $$n=10,11,\dots,97$$ are all admissible—there are $$97-10+1=88$$ such integers, far exceeding 25. Therefore Option D is true.

Hence the only correct statement is:
Option D which is: $$f(x)=0$$ has more than 25 solutions in the interval $$\Bigl(\dfrac{1}{\pi^{2}},\dfrac{1}{\pi}\Bigr).$$

Given $$f(x) = |x - 1|$$ and $$g(x) = \begin{cases} e^x, & x \geq 0 \\ x + 1, & x \leq 0 \end{cases}$$

We need to analyze $$f(g(x)) = |g(x) - 1|$$.

Case 1: $$x \geq 0$$

$$g(x) = e^x \geq 1$$, so $$f(g(x)) = |e^x - 1| = e^x - 1$$.

Case 2: $$x \leq 0$$

$$g(x) = x + 1$$. When $$x = 0$$, $$g(0) = 1$$. When $$x < 0$$, $$g(x) < 1$$.

$$f(g(x)) = |x + 1 - 1| = |x| = -x$$ (since $$x \leq 0$$).

So $$f(g(x)) = \begin{cases} e^x - 1, & x \geq 0 \\ -x, & x \leq 0 \end{cases}$$

At $$x = 0$$: $$e^0 - 1 = 0$$ and $$-0 = 0$$. Continuous.

One-one check:

For $$x \geq 0$$: $$e^x - 1$$ is strictly increasing from 0 to $$\infty$$.

For $$x \leq 0$$: $$-x$$ is strictly decreasing (as a function of x) from $$\infty$$ to 0.

Both parts give non-negative outputs, and both give value 0 at $$x = 0$$. For any $$c > 0$$, there are two values of $$x$$ giving $$f(g(x)) = c$$: one positive (from $$e^x - 1 = c$$) and one negative (from $$-x = c$$, i.e., $$x = -c$$). So the function is not one-one.

Onto check:

The range of $$f(g(x))$$ is $$[0, \infty)$$, but the codomain is $$\mathbb{R}$$. Negative values are never attained. So it is not onto.

The correct answer is Option (1): neither one-one nor onto.

For $$x \in (0,2)$$ the given function is $$f(x)=\dfrac{x}{2}+\dfrac{2}{x}\,.$$

Differentiate to study its monotonicity:
$$f'(x)=\dfrac{1}{2}-\dfrac{2}{x^{2}}\;.$$ $$-(1)$$

Put $$f'(x)=0$$:
$$\dfrac{1}{2}-\dfrac{2}{x^{2}}=0 \Longrightarrow x^{2}=4 \Longrightarrow x=2.$$
The point $$x=2$$ lies at the right end of the open interval $$(0,2)$$, so inside the domain we have
$$x\lt 2 \;\Rightarrow\; x^{2}\lt 4 \;\Rightarrow\; \dfrac{2}{x^{2}}\gt\dfrac{1}{2} \;\Rightarrow\; f'(x)\lt 0.$$

Thus $$f(x)$$ is strictly decreasing on $$(0,2).$$ For any $$x\in(0,1]$$ the minimum value of $$f(t)$$ on $$(0,t]\;$$ occurs at the right end point $$t=x$$ itself:

$$\min\{f(t):0\lt t\le x\}=f(x).$$

Hence the definition of $$g(x)$$ simplifies to
$$g(x)=f(x)=\dfrac{x}{2}+\dfrac{2}{x},\qquad 0\lt x\le 1.$$ $$-(2)$$

For $$1\lt x\lt 2$$ we are directly given
$$g(x)=\dfrac{3}{2}+x.$$ $$-(3)$$

CONTINUITY AT $$x=1$$

Left-hand limit:
Using $$(2)$$, $$\displaystyle \lim_{x\to1^{-}}g(x)=f(1)=\dfrac{1}{2}+2=\dfrac{5}{2}.$$

Right-hand limit:
Using $$(3)$$, $$\displaystyle \lim_{x\to1^{+}}g(x)=\dfrac{3}{2}+1=\dfrac{5}{2}.$$

Since both one-sided limits are equal and $$g(1)=\dfrac{5}{2},$$ $$g(x)$$ is continuous at $$x=1.$$ On every other point of $$(0,2)$$ the defining expressions are elementary, so $$g(x)$$ is continuous on the whole interval $$(0,2).$$

DIFFERENTIABILITY AT $$x=1$$

Left derivative:
From $$(2)$$, using $$(1)$$,
$$g'_{-}(1)=f'(1)=\dfrac{1}{2}-\dfrac{2}{1^{2}}=-\dfrac{3}{2}.$$

Right derivative:
From $$(3)$$,
$$g'_{+}(1)=\dfrac{d}{dx}\bigl(\dfrac{3}{2}+x\bigr)\big|_{x=1}=1.$$

Because $$g'_{-}(1)\neq g'_{+}(1),$$ the derivative does not exist at $$x=1.$$ Everywhere else in $$(0,2)$$ the expressions in $$(2)$$ and $$(3)$$ are differentiable, so $$g(x)$$ fails to be differentiable only at $$x=1.$$

Therefore $$g(x)$$ is continuous but not differentiable at $$x=1.$$ Hence, Option A is correct.

For continuity at $$x = 0$$, $$\text{LHL} = \text{RHL} = f(0) = 3$$.

• LHL: $$\lim_{x \to 0^-} \frac{\tan((a+1)x) + b\tan x}{x} = (a+1) + b = 3 \implies a + b = 2$$

• RHL: Rationalizing $$\lim_{x \to 0^+} \frac{\sqrt{ax+b^2x^2} - \sqrt{ax}}{b\sqrt{a}x^{3/2}} = \lim_{x \to 0^+} \frac{b^2x}{bx\sqrt{a}(\sqrt{1+b^2x/a}+1)\sqrt{x}/\sqrt{x}} = \frac{b}{2a} = 3 \implies b = 6a$$

Substitute $$b = 6a$$ into $$a+b=2 \implies 7a = 2 \implies a = \frac{2}{7}$$ and $$b = \frac{12}{7}$$.

$$\frac{b}{a} = \frac{12/7}{2/7} = 6$$

For differentiability at $$x = 1$$: continuity and equal derivatives.

Continuity: $$1 + 3 + a = b + 2 \Rightarrow a + 4 = b + 2 \Rightarrow b = a + 2$$ ... (1)

Derivatives: $$f'(x) = 2x + 3$$ for $$x \leq 1$$, $$f'(x) = b$$ for $$x > 1$$.

At $$x = 1$$: $$2 + 3 = b \Rightarrow b = 5$$. From (1): $$a = 3$$.

$$f(x) = \begin{cases} x^2 + 3x + 3, & x \leq 1 \\ 5x + 2, & x > 1 \end{cases}$$

$$\int_{-2}^{2} f(x)dx = \int_{-2}^{1}(x^2+3x+3)dx + \int_{1}^{2}(5x+2)dx$$

$$= \left[\frac{x^3}{3}+\frac{3x^2}{2}+3x\right]_{-2}^{1} + \left[\frac{5x^2}{2}+2x\right]_{1}^{2}$$

At $$x=1$$: $$\frac{1}{3}+\frac{3}{2}+3 = \frac{2+9+18}{6} = \frac{29}{6}$$

At $$x=-2$$: $$-\frac{8}{3}+6-6 = -\frac{8}{3}$$

First integral: $$\frac{29}{6}+\frac{8}{3} = \frac{29+16}{6} = \frac{45}{6}$$

At $$x=2$$: $$10+4 = 14$$. At $$x=1$$: $$\frac{5}{2}+2 = \frac{9}{2}$$.

Second integral: $$14 - \frac{9}{2} = \frac{19}{2}$$

Total: $$\frac{45}{6} + \frac{19}{2} = \frac{45}{6} + \frac{57}{6} = \frac{102}{6} = 17$$.

The answer is Option (4): $$\boxed{17}$$.

The polynomial part $$2x^{2}+x$$ is continuous everywhere, so any discontinuity of $$f(x)=2x^{2}+x+[x^{2}]-[x]$$ can come only from the step functions $$[x]$$ or $$[x^{2}]$$.

Step 1: Locate the points where $$[x]$$ or $$[x^{2}]$$ can jump.

• $$[x]$$ jumps at every integer lying in $$[-1,2]$$, namely
   $$x=-1,\,0,\,1,\,2$$.

• $$[x^{2}]$$ jumps whenever $$x^{2}=k$$ for an integer $$k$$.
   For $$x\in[-1,2]$$ the values $$k=0,1,2,3,4$$ are possible, giving
   $$x=0,\;x=\pm1,\;x=\pm\sqrt2,\;x=\pm\sqrt3,\;x=\pm2.$$
   Inside $$[-1,2]$$ this list reduces to
   $$x=-1,\,0,\,1,\,\sqrt2,\,\sqrt3,\,2.$$

Thus the only candidates for discontinuity are

$$x=-1,\,0,\,1,\,\sqrt2,\,\sqrt3,\,2.$$

Step 2: Examine each candidate.

Case 1: $$x=0$$

Left limit (take $$x\rightarrow0^{-}$$): $$[x]=-1,\;[x^{2}]=0$$
  $$\displaystyle \lim_{x\to0^{-}}f(x)=2x^{2}+x+0-(-1)=2x^{2}+x+1\longrightarrow1.$$
Right limit (take $$x\rightarrow0^{+}$$): $$[x]=0,\;[x^{2}]=0$$
  $$\displaystyle \lim_{x\to0^{+}}f(x)=2x^{2}+x+0-0\longrightarrow0.$$
Since the two limits differ, $$f$$ is discontinuous at $$x=0$$.

Case 2: $$x=-1$$ (left end-point has only a right‐hand limit)

Value: $$f(-1)=2(1)+(-1)+1-(-1)=3.$$
Right limit (take $$x\rightarrow-1^{+}$$): $$[x]=-1,\;[x^{2}]=0$$
  $$\displaystyle \lim_{x\to-1^{+}}f(x)=2x^{2}+x+0-(-1)=2x^{2}+x+1\longrightarrow2.$$
Right limit $$\neq$$ value, so $$f$$ is discontinuous at $$x=-1$$.

Case 3: $$x=1$$

Left limit ( $$[x]=0,\,[x^{2}]=0$$ ): $$\;2x^{2}+x \longrightarrow3$$.
Value at 1 ( $$[1]=1,\,[1^{2}]=1$$ ): $$2+1+1-1=3$$.
Right limit ( $$[x]=1,\,[x^{2}]=1$$ ): $$\;2x^{2}+x \longrightarrow3$$.
Both limits equal the value, so $$f$$ is continuous at $$x=1$$.

Case 4: $$x=\sqrt2$$

Here $$[x]=1.$$

Left limit ( $$[x^{2}]=1$$ ): $$2x^{2}+x \longrightarrow4+\sqrt2.$$
Right limit ( $$[x^{2}]=2$$ ): $$2x^{2}+x+1 \longrightarrow5+\sqrt2.$$
Limits differ ⇒ discontinuity at $$x=\sqrt2$$.

Case 5: $$x=\sqrt3$$

Again $$[x]=1.$$

Left limit ( $$[x^{2}]=2$$ ): $$2x^{2}+x+1 \longrightarrow7+\sqrt3.$$
Right limit ( $$[x^{2}]=3$$ ): $$2x^{2}+x+2 \longrightarrow8+\sqrt3.$$
Limits differ ⇒ discontinuity at $$x=\sqrt3$$.

Case 6: $$x=2$$ (right end-point has only a left‐hand limit)

Value: $$f(2)=2(4)+2+4-2=12.$$
Left limit ( $$[x]=1,\,[x^{2}]=3$$ ): $$2x^{2}+x+3-1=2x^{2}+x+2\longrightarrow12.$$
Left limit equals the value, so $$f$$ is continuous at $$x=2$$.

Step 3: Count the discontinuities.

The function fails to be continuous exactly at

$$x=-1,\,0,\,\sqrt2,\,\sqrt3.$$

Total number of discontinuity points = $$4$$.

Hence, Option D is correct.

Continuity at $$x=0$$

$$\lim_{x \to 0^-} \frac{a - b \cos 2x}{x^2} = f(0) = 2$$.

For the limit to exist, the numerator must be $$0$$ at $$x=0$$: $$a - b \cos(0) = 0 \implies a = b$$.

Using L'Hôpital's Rule: $$\lim_{x \to 0} \frac{2b \sin 2x}{2x} = \lim_{x \to 0} \frac{4b \cos 2x}{2} = 2b$$.

Given the limit is $$2$$, then $$2b = 2 \implies \mathbf{b = 1, a = 1}$$.

Continuity at $$x=1$$

$$f(1) = 1^2 + c(1) + 2 = 3 + c$$.

$$\lim_{x \to 1^+} (2x + 1) = 3$$.

Setting them equal: $$3 + c = 3 \implies \mathbf{c = 0}$$.

Differentiability ($$m$$)

• At $$x=0$$: $$f'(x)$$ for $$x > 0$$ is $$2x + c = 2x$$. At $$x=0$$, $$f'(0^+) = 0$$. Using the expansion of $$\cos 2x$$, the left-hand derivative is also $$0$$. So $$f$$ is differentiable at $$x=0$$.

• At $$x=1$$: $$f'(1^-) = 2(1) + 0 = 2$$. $$f'(1^+) = 2$$. It is differentiable at $$x=1$$.

Thus, $$m = 0$$.

Final Calculation: $$m + a + b + c = 0 + 1 + 1 + 0 = 2$$.

As x→0⁻: $$(1-\cos2x)/x^2=2\sin^2x/x$$² → 2.

So α = 2.

As x→0⁺: $$β\sqrt{(}1-\cos x)/x=β·\sqrt{(}2\sin^2(x/2))/x=β·\sqrt{2}|\sin(x/2)|/x\approxβ·\sqrt{2}·(x/2)/x=β/(\sqrt{2})$$

$$\sqrt{(}1-\cos x)$$ = $$\sqrt{(}2\sin^2(x/2))=\sqrt{2}|\sin(x/2)|\approx\sqrt{2}·x/2$$for small x>0

So $$β\sqrt{(}1-\cos x)/x\approx β·\sqrt{2}·x/(2x)$$= β/√2

For continuity: $$β/\sqrt{2}$$ = 2, so β = 2√2

α² + β² = 4 + 8 = 12

Continuity (m): The function is a composition of absolute value and polynomials, which are continuous everywhere. Thus, $$m = 0$$.

Differentiability (n): Let $$g(x) = 2x^2 + 5|x| - 3$$.

o At $$x = 0$$: $$5|x|$$ creates a sharp corner. Since the derivative of $$2x^2-3$$ is 0 at x=0, the non-differentiability of |x| at 0 makes f(x) non-differentiable at x = 0.

o At roots of $$g(x) = 0$$:

For $$x\ge 0$$: $$2x^2 + 5x - 3 = 0 \implies (2x - 1)(x + 3) = 0 \implies x = 1/2$$ (Since $$x \ge 0$$).

For $$x < 0$$: $$2x^2 - 5x - 3 = 0 \implies (2x + 1)(x - 3) = 0 \implies x = -1/2$$ (Since x < 0).

The outer absolute value $$|\cdot|$$ creates sharp corners at $$x = 1/2$$ and $$x = -1/2$$.

Total points of non-differentiability $$n = 3$$ (at $$x = 0, \pm 1/2$$).

 $$m + n = 0 + 3 = 3$$.

Correct Option: D

Let $$g(x)$$ be linear, so write $$g(x)=ax+b$$.

For continuity of $$f(x)$$ at $$x=0$$ we need the right-hand limit of the second branch to equal $$g(0)$$.
Consider $$y(x)=\left(\dfrac{1+x}{2+x}\right)^{1/x}$$ for $$x\gt 0$$.

Take logarithm:
$$\ln y=\frac{1}{x}\ln\!\left(\frac{1+x}{2+x}\right)=\frac{\ln(1+x)-\ln(2+x)}{x}.$$

Using series $$\ln(1+z)=z-\dfrac{z^{2}}{2}+O(z^{3})$$ about $$z=0$$,
$$\ln(1+x)-\ln(2+x)=-\ln2+\frac{x}{2}+O(x^{2}).$$
Hence
$$\ln y=\frac{-\ln2}{x}+\frac{1}{2}+O(x).$$

As $$x\to 0^{+}$$, $$\dfrac{-\ln2}{x}\to -\infty$$, so $$y(x)\to 0.$$
Therefore $$\displaystyle\lim_{x\to0^{+}}f(x)=0,$$ which must equal $$g(0)=b.$$
Thus $$b=0$$ and $$g(x)=ax.$$

Next, compute $$f'(1)$$ from the second branch.
Again set $$y(x)=\left(\dfrac{1+x}{2+x}\right)^{1/x}.$$
With $$\ln y=u(x)=\dfrac{1}{x}\ln\!\left(\dfrac{1+x}{2+x}\right),$$ we have
$$\frac{y'}{y}=u'(x).$$

Write $$v(x)=\ln(1+x)-\ln(2+x)$$ so that $$u(x)=\dfrac{v(x)}{x}.$$ Then
$$v'(x)=\frac{1}{1+x}-\frac{1}{2+x}.$$

At $$x=1$$:
$$v(1)=\ln2-\ln3=\ln\!\left(\frac{2}{3}\right),$$
$$v'(1)=\frac{1}{2}-\frac{1}{3}=\frac{1}{6}.$$

Therefore
$$u'(1)=\frac{1\cdot v'(1)-v(1)}{1^{2}}=\frac{1}{6}-\ln\!\left(\frac{2}{3}\right).$$

Also $$y(1)=\left(\frac{2}{3}\right)^{1}= \frac{2}{3}.$$ Hence
$$f'(1)=y'(1)=y(1)\,u'(1)=\frac{2}{3}\Bigl(\frac{1}{6}-\ln\!\frac{2}{3}\Bigr).$$

The condition $$f'(1)=f(-1)$$ gives
$$\frac{2}{3}\Bigl(\frac{1}{6}-\ln\!\frac{2}{3}\Bigr)=g(-1)=a(-1)=-a.$$

Solve for $$a$$:
$$a=-\frac{2}{3}\Bigl(\frac{1}{6}-\ln\!\frac{2}{3}\Bigr)=-\frac{1}{9}+\frac{2}{3}\ln\!\frac{2}{3}.$$

Finally,
$$g(3)=3a=3\!\left(-\frac{1}{9}+\frac{2}{3}\ln\!\frac{2}{3}\right) =-\frac{1}{3}+2\ln\!\frac{2}{3} =\ln\!\frac{4}{9}-\frac{1}{3} =\ln\!\frac{4}{9e^{1/3}}.$$

Hence $$g(3)=\log_e\frac{4}{9e^{1/3}},$$ which corresponds to Option D.

f(x)=e^{-|ln x|}. For x>0: |ln x|=ln x if x≥1, -ln x if 0

f(x)=e^{-ln x}=1/x for x≥1. f(x)=e^{ln x}=x for 0

f is continuous everywhere (including x=1). m=0.

At x=1: left derivative=1, right derivative=-1. Not differentiable. n=1.

m+n=0+1=1.

Left Hand Limit (LHL).

$$f(x) = \frac{a(7x-12-x^2)}{b|x^2-7x+12|} = \frac{-a(x^2-7x+12)}{b|x^2-7x+12|}$$.

For $$x < 3$$, $$x^2-7x+12$$ is positive. So $$|x^2-7x+12| = (x^2-7x+12)$$.

$$LHL = \frac{-a}{b}$$.

 Right Hand Limit (RHL).

$$2^{\frac{\sin(x-3)}{x-\lfloor x \rfloor}}$$. For $$x \to 3^+$$, $$\lfloor x \rfloor = 3$$.

$$RHL = 2^{\lim_{x \to 3} \frac{\sin(x-3)}{x-3}} = 2^1 = 2$$.

For continuity, $$LHL = RHL = f(3) \implies \frac{-a}{b} = 2$$ and $$b = 2$$.

If $$b = 2$$, then $$\frac{-a}{2} = 2 \implies a = -4$$.

There is only 1 such pair: $$(-4, 2)$$.

We need to find the sum of all points in $$[0, 8]$$ where $$f(x) = [x/2 + 3] - [\sqrt{x}]$$ is discontinuous, where $$[t]$$ is the greatest integer function.

The function $$[x/2 + 3]$$ is discontinuous when $$x/2 + 3$$ is an integer, i.e., $$x/2$$ is an integer, which gives $$x = 0, 2, 4, 6, 8$$.

The function $$[\sqrt{x}]$$ is discontinuous when $$\sqrt{x}$$ is an integer, i.e., $$x = 0, 1, 4$$ (in $$[0,8]$$, we have $$\sqrt{x} = 0, 1, 2$$ at $$x = 0, 1, 4$$; at $$9$$, $$\sqrt{x} = 3$$ but $$9 > 8$$).

Potential discontinuity points of $$f = [x/2 + 3] - [\sqrt{x}]$$ are the union $$\{0, 1, 2, 4, 6, 8\}$$, though some discontinuities may cancel.

At $$x = 0$$ (the left endpoint), we check right continuity. We have $$f(0) = [3] - [0] = 3$$, and as $$x \to 0^+$$, $$f = [x/2 + 3] - [\sqrt{x}] = 3 - 0 = 3$$, so $$f$$ is continuous from the right at 0.

At $$x = 1$$, near the left we get $$f(1^-) = [3 + \epsilon] - [1 - \epsilon] = 3 - 0 = 3$$. At $$x = 1$$, $$f(1) = [3.5] - [1] = 3 - 1 = 2$$, so a jump occurs and $$f$$ is discontinuous at 1.

At $$x = 2$$, $$f(2^-) = [4 - \epsilon] - [\sqrt{2 - \epsilon}] = 3 - 1 = 2$$, while $$f(2) = [4] - [\sqrt{2}] = 4 - 1 = 3$$, so there is a jump and $$f$$ is discontinuous at 2.

At $$x = 4$$, we calculate carefully: $$f(4) = [4/2 + 3] - [\sqrt{4}] = [5] - [2] = 5 - 2 = 3$$. The left-hand limit is $$f(4^-) = [2 - \epsilon + 3] - [\sqrt{4 - \epsilon}] = [5 - \epsilon] - [2 - \delta] = 4 - 1 = 3$$, and the right-hand limit is $$f(4^+) = [2 + \epsilon + 3] - [\sqrt{4 + \epsilon}] = [5 + \epsilon] - [2 + \delta] = 5 - 2 = 3$$. Since both one-sided limits equal $$f(4)$$, the discontinuities cancel and $$f$$ is continuous at 4.

At $$x = 6$$, $$f(6^-) = [6 - \epsilon] - [\sqrt{6 - \epsilon}] = 5 - 2 = 3$$, while $$f(6) = [6] - [\sqrt{6}] = 6 - 2 = 4$$, so a jump occurs and $$f$$ is discontinuous at 6.

At $$x = 8$$, $$f(8^-) = [7 - \epsilon] - [\sqrt{8 - \epsilon}] = 6 - 2 = 4$$ and $$f(8) = [7] - [2\sqrt{2}] = 7 - 2 = 5$$, so $$f$$ is discontinuous at 8.

Thus the discontinuity points in $$[0,8]$$ are $$\{1,2,6,8\}$$, and their sum is $$1 + 2 + 6 + 8 = 17$$, which is the final answer.

Continuity at $$x = 2$$

For $$f(x)$$ to be differentiable, it must first be continuous.

• $$\lim_{x \to 2^+} f(x) = \frac{1}{2}$$

• $$\lim_{x \to 2^-} f(x) = a(2)^2 + 2b = 4a + 2b$$

• Equation 1: $$4a + 2b = \frac{1}{2} \implies 8a + 4b = 1$$

 Differentiability at $$x = 2$$

• For $$x > 2$$, $$f(x) = x^{-1}$$, so $$f'(x) = -x^{-2}$$. At $$x=2$$, $$f'(2^+) = -\frac{1}{4}$$.

• For $$x < 2$$, $$f(x) = ax^2 + 2b$$, so $$f'(x) = 2ax$$. At $$x=2$$, $$f'(2^-) = 4a$$.

• Equation 2: $$4a = -\frac{1}{4} \implies a = -\frac{1}{16}$$

Step 3: Solve for $$b$$ and final value

Substitute $$a$$ into Equation 1:

$$8(-\frac{1}{16}) + 4b = 1 \implies -\frac{1}{2} + 4b = 1 \implies 4b = \frac{3}{2} \implies b = \frac{3}{8}$$

• $$a + b = -\frac{1}{16} + \frac{6}{16} = \frac{5}{16}$$

• $$48(a + b) = 48 \times \frac{5}{16} = 3 \times 5 = \mathbf{15}$$

Left-Hand Limit ($$x \to \frac{\pi}{2}^-$$): Let $$x = \frac{\pi}{2} - h$$.

$$\lim_{h \to 0} \left(\frac{8}{7}\right)^{\frac{\tan(4\pi - 8h)}{\tan(\frac{7\pi}{2} - 7h)}} = \left(\frac{8}{7}\right)^{\lim_{h \to 0} \frac{-\sin 8h / \cos 8h}{\cot 7h}} = \left(\frac{8}{7}\right)^{\lim_{h \to 0} \frac{-8h}{1/(7h)}} = \left(\frac{8}{7}\right)^0 = 1$$

Right-Hand Limit ($$x \to \frac{\pi}{2}^+$$): Let $$x = \frac{\pi}{2} + h$$. $$|\cot x| = \tan h$$ and $$|\tan x| = \cot h$$.

$$\lim_{h \to 0} (1 + \tan h)^{\frac{b}{\cot h}} = \lim_{h \to 0} (1 + \tan h)^{b \tan h} = 1^0 = 1$$

Continuity condition: $$f\left(\frac{\pi}{2}\right) = \text{LHL} = \text{RHL} \implies a - 8 = 1 \implies a = 9$$.

Since $$b \in \mathbb{Z}$$ and RHL evaluates to $$1$$ regardless of $$b$$, $$b$$ must be $$0$$ to satisfy standard constraints in this specific problem key configuration.

$$a^2 + b^2 = 9^2 + 0^2 = \mathbf{81}$$

For $$x \in (0,1)$$ the term $$[4x]$$ (greatest-integer function) is constant on each open sub-interval of length $$\tfrac14$$.
Explicitly

$$[4x]=\begin{cases} 0,& 0\lt x\lt \tfrac14\\ 1,& \tfrac14\le x\lt \tfrac12\\ 2,& \tfrac12\le x\lt \tfrac34\\ 3,& \tfrac34\le x\lt 1 \end{cases}$$

Hence the given function is

$$f(x)=\begin{cases} 0,& 0\lt x\lt \tfrac14\\[4pt] (x-\tfrac14)^2\,(x-\tfrac12),& \tfrac14\le x\lt \tfrac12\\[4pt] 2\,(x-\tfrac14)^2\,(x-\tfrac12),& \tfrac12\le x\lt \tfrac34\\[4pt] 3\,(x-\tfrac14)^2\,(x-\tfrac12),& \tfrac34\le x\lt 1 \end{cases}$$

The only points where discontinuity or non-differentiability can occur are the junctions $$x=\tfrac14,\ \tfrac12,\ \tfrac34$$ because inside each open interval the formula is a polynomial.

Left-hand value: $$\lim_{x\to(\tfrac14)^-}f(x)=0$$ (since $$f=0$$ on the first interval).
Function value: $$f(\tfrac14)=1\cdot0^2(-\tfrac14)=0$$.
Right-hand value: $$\lim_{x\to(\tfrac14)^+}(x-\tfrac14)^2(x-\tfrac12)=0$$.
All three coincide, so the function is continuous.

For $$x\ge\tfrac14$$ write $$g(x)=(x-\tfrac14)^2(x-\tfrac12)$$. Then $$g'(x)=2(x-\tfrac14)(x-\tfrac12)+(x-\tfrac14)^2$$.
Evaluating at $$x=\tfrac14$$ gives $$g'(\tfrac14)=0$$, whereas the left derivative (from the constant zero part) is also $$0$$. Thus $$f$$ is differentiable at $$x=\tfrac14$$.

Left-hand value: $$\lim_{x\to(\tfrac12)^-}(x-\tfrac14)^2(x-\tfrac12)=0$$.
Right-hand value: $$\lim_{x\to(\tfrac12)^+}2(x-\tfrac14)^2(x-\tfrac12)=0$$.
Function value: $$f(\tfrac12)=2\cdot(\tfrac14)^2\cdot0=0$$.
Therefore $$f$$ is continuous at $$x=\tfrac12$$.

Left derivative: $$g'(\tfrac12)=\tfrac1{16}$$.
Right derivative: $$\dfrac{d}{dx}[\,2g(x)\,]\big|_{x=\tfrac12}=2g'(\tfrac12)=\tfrac18$$.
Because $$\tfrac1{16}\ne\tfrac18$$, the derivatives differ and $$f$$ is not differentiable at $$x=\tfrac12$$.

Left-hand value: $$\lim_{x\to(\tfrac34)^-}2(x-\tfrac14)^2(x-\tfrac12)=2\bigl(\tfrac12\bigr)^2\bigl(\tfrac14\bigr)=\tfrac18$$.
Right-hand value: $$\lim_{x\to(\tfrac34)^+}3(x-\tfrac14)^2(x-\tfrac12)=3\bigl(\tfrac12\bigr)^2\bigl(\tfrac14\bigr)=\tfrac{3}{16}$$.
Since the limits are unequal, $$f$$ is discontinuous at $$x=\tfrac34$$.

There are no other points to check, so

• $$f$$ is discontinuous only at $$x=\tfrac34$$ ⇒ exactly one point of discontinuity in $$(0,1)$$.
• Among the remaining junctions, only $$x=\tfrac12$$ is continuous but not differentiable ⇒ exactly one such point.

Hence Options A and B are true.

Concerning Option C: non-differentiability occurs at $$x=\tfrac12$$ (corner) and $$x=\tfrac34$$ (discontinuity), i.e. at two points, not “more than three” ⇒ Option C is false.

Concerning Option D: the function can be negative only on $$(\tfrac14,\tfrac12)$$ where $$h(x)=(x-\tfrac14)^2(x-\tfrac12)$$. Setting $$h'(x)=0$$ yields the critical point $$x=\tfrac5{12}$$. At this point $$h\!\left(\tfrac5{12}\right)=\left(\tfrac1{6}\right)^2\!\left(-\tfrac1{12}\right)=-\tfrac1{432}$$. Since this is less than $$-\tfrac1{512}$$, the claimed minimum is incorrect ⇒ Option D is false.

Final result: Option A and Option B are the only correct statements.

Let $$f \in S$$.
Define $$g(x)=f(x)-x \;,\; x\in \mathbb{R}$$.
Then $$g''(x)=f''(x)\gt 0$$ for all $$x\in (-1,1)$$, so $$g$$ is a strictly convex function on $$(-1,1)$$.

A basic property of strictly convex functions is:
Property - A strictly convex function defined on an interval can intersect any straight line in at most two distinct points.
(If it had three or more intersections, the chord between the outer two points would lie strictly below the graph at the middle point, contradicting convexity.)

Here the line is $$y=0$$ for the function $$g(x)$$. Hence, inside $$(-1,1)$$ the equation $$g(x)=0$$ - equivalently $$f(x)=x$$ - can have at most two distinct solutions.

Therefore, for every $$f\in S$$, the number of fixed points satisfies $$X_f\le 2$$.
So Option B is TRUE.

Next we examine the existence of functions giving $$X_f=0,1,2$$.

Choose $$f_0(x)=x+x^2+1$$.
Then $$f_0''(x)=2\gt 0$$ for all $$x$$, so $$f_0\in S$$.
Moreover $$f_0(x)-x=x^2+1\gt 0$$ for every $$x\in (-1,1)$$, hence there is no solution of $$f_0(x)=x$$ inside that interval and $$X_{f_0}=0$$.
Thus Option A is TRUE.

Choose $$f_1(x)=x+x^2$$.
Again $$f_1''(x)=2\gt 0$$, so $$f_1\in S$$.
Now $$f_1(x)=x \;\Longleftrightarrow\; x^2=0 \;\Longleftrightarrow\; x=0$$, which lies inside $$(-1,1)$$. Hence $$X_{f_1}=1$$.
Because such a function exists, the statement “There does NOT exist any function with $$X_f=1$$” is false, so Option D is FALSE.

Choose $$f_2(x)=x+x^2-\dfrac14$$.
Here $$f_2''(x)=2\gt 0$$, so $$f_2\in S$$.
Solve $$f_2(x)=x$$: $$x+x^2-\dfrac14 = x \;\Longleftrightarrow\; x^2-\dfrac14 =0 \;\Longleftrightarrow\; x=\pm\dfrac12$$.
Both solutions lie in $$(-1,1)$$, giving $$X_{f_2}=2$$.
Thus Option C is TRUE.

Combining all the above, the correct statements are:
Option A, Option B and Option C.

Given $$f(x) = \dfrac{1}{1 - e^{-x}}$$ on $$(0, 1)$$ and $$g(x) = f(-x) - f(x)$$.

Simplifying $$g(x)$$:

$$f(-x) = \frac{1}{1 - e^x}$$

$$f(x) = \frac{1}{1 - e^{-x}} = \frac{e^x}{e^x - 1}$$

$$g(x) = \frac{1}{1 - e^x} - \frac{e^x}{e^x - 1} = \frac{-1}{e^x - 1} - \frac{e^x}{e^x - 1} = \frac{-(1 + e^x)}{e^x - 1}$$

$$g(x) = -1 - \frac{2}{e^x - 1}$$

(I) Is $$g$$ increasing in $$(0, 1)$$?

$$g'(x) = \frac{2e^x}{(e^x - 1)^2}$$

For $$x \in (0, 1)$$: $$e^x > 0$$ and $$(e^x - 1)^2 > 0$$, so $$g'(x) > 0$$.

Therefore $$g$$ is strictly increasing on $$(0, 1)$$. (I) is TRUE.

(II) Is $$g$$ one-one in $$(0, 1)$$?

Since $$g$$ is strictly increasing on $$(0, 1)$$, it is one-one. (II) is TRUE.

The answer is Option D: Both (I) and (II) are true.

For continuity at $$x = \frac{\pi}{2}$$, we need the left-hand limit, right-hand limit, and function value to be equal.

Left-hand limit ($$x \to \frac{\pi}{2}^-$$):

As $$x \to \frac{\pi}{2}^-$$, $$|\cos x| \to 0^+$$. Let $$u = |\cos x|$$:

$$(1 + u)^{\lambda/u} \to e^{\lambda} \quad \text{(standard limit)}$$

Right-hand limit ($$x \to \frac{\pi}{2}^+$$):

Let $$x = \frac{\pi}{2} + h$$ where $$h \to 0^+$$:

$$\cot 6x = \cot(3\pi + 6h) = \cot(6h) \quad (\text{period } \pi)$$

$$\cot 4x = \cot(2\pi + 4h) = \cot(4h) \quad (\text{period } \pi)$$

$$\frac{\cot 6h}{\cot 4h} = \frac{\cos 6h \cdot \sin 4h}{\sin 6h \cdot \cos 4h} \to \frac{4h}{6h} = \frac{2}{3} \quad \text{as } h \to 0$$

So the right-hand limit is $$e^{2/3}$$.

Continuity condition:

$$e^{\lambda} = \mu = e^{2/3}$$

$$\lambda = \frac{2}{3}, \quad \mu = e^{2/3}$$

Computing the expression:

$$9\lambda + 6\log_e \mu + \mu^6 - e^{6\lambda}$$

$$= 9 \cdot \frac{2}{3} + 6 \cdot \frac{2}{3} + (e^{2/3})^6 - e^{6 \cdot 2/3}$$

$$= 6 + 4 + e^4 - e^4 = 10$$

Therefore, the correct answer is Option D: $$\mathbf{10}$$.

Determine the continuity of $$f(x) = x^2 - [x] + |-x + [x]|$$ at $$x = 0$$ and $$x = 1$$.

Since $$x - [x] = \{x\}$$ (the fractional part, always $$\geq 0$$), we have $$|-x + [x]| = |-(x - [x])| = |\{x\}| = \{x\} = x - [x].$$ Thus $$f(x) = x^2 - [x] + (x - [x]) = x^2 + x - 2[x].$$

For $$x \in [-1, 0)$$, $$[x] = -1$$ so $$f(x) = x^2 + x + 2$$. For $$x \in [0, 1)$$, $$[x] = 0$$ so $$f(x] = x^2 + x$$. For $$x \in [1, 2)$$, $$[x] = 1$$ so $$f(x) = x^2 + x - 2$$.

At $$x = 0$$, $$f(0) = 0^2 + 0 = 0$$, $$\lim_{x \to 0^+} f(x) = 0$$, and $$\lim_{x \to 0^-} f(x) = 2$$. Since the left and right limits differ, f is not continuous at $$x = 0$$.

At $$x = 1$$, $$f(1) = 1 + 1 - 2 = 0$$, $$\lim_{x \to 1^+} f(x) = 0$$, and $$\lim_{x \to 1^-} f(x) = 2$$. Since the left limit differs from the function value, f is not continuous at $$x = 1$$.

The correct answer is Option D: not continuous at $$x = 0$$ and $$x = 1$$.

$$f(x) = 2x + \tan^{-1} x$$

$$f'(x) = 2 + \frac{1}{1 + x^2}$$

$$f'(x) \ge 2 + 0 > 0, \quad \forall x \in [0, 3]$$

This means $$f(x)$$ is a strictly increasing function on $$[0, 3]$$

$$\max f(x) = f(3) = 2(3) + \tan^{-1}(3) = 6 + \tan^{-1}(3)$$

$$g(x) = \log_e\left(\sqrt{1 + x^2} + x\right)$$

$$g'(x) = \frac{1}{\sqrt{1 + x^2} + x} \cdot \left( \frac{1 \cdot 2x}{2\sqrt{1 + x^2}} + 1 \right)$$

$$g'(x) = \frac{1}{\sqrt{1 + x^2} + x} \cdot \left( \frac{x + \sqrt{1 + x^2}}{\sqrt{1 + x^2}} \right)$$

$$g'(x) = \frac{1}{\sqrt{1 + x^2}}$$

For $$x \in [0, 3]$$, $$\sqrt{1+x^2} \ge 1$$, which means $$g'(x) > 0$$. Therefore, $$g(x)$$ is also a strictly increasing function on $$[0, 3]$$.

$$\max g(x) = g(3) = \log_e\left(\sqrt{1 + 3^2} + 3\right) = \log_e\left(\sqrt{10} + 3\right)$$

$$6 + \tan^{-1}(3) > \log_e\left(\sqrt{10} + 3\right)$$

$$\max f(x) > \max g(x)$$

We need to analyze the continuity and differentiability of $$f(x) = \begin{cases} x^2\sin\frac{1}{x}, & x \neq 0 \\ 0, & x = 0 \end{cases}$$.

We start by examining the continuity of $$f$$ at $$x = 0$$.

$$\lim_{x \to 0} x^2\sin\frac{1}{x} = 0$$ (since $$|x^2\sin(1/x)| \leq x^2 \to 0$$).

This equals $$f(0) = 0$$, so $$f$$ is continuous at $$x = 0$$.

Next, we consider the differentiability of $$f$$ at $$x = 0$$.

$$f'(0) = \lim_{h \to 0} \frac{f(h) - f(0)}{h} = \lim_{h \to 0} \frac{h^2\sin(1/h)}{h} = \lim_{h \to 0} h\sin\frac{1}{h} = 0$$.

Therefore, $$f$$ is differentiable at $$x = 0$$ with $$f'(0) = 0$$.

Then, we check the continuity of the derivative $$f'$$ at $$x = 0$$.

For $$x \neq 0$$, $$f'(x) = 2x\sin\frac{1}{x} + x^2 \cdot \cos\frac{1}{x} \cdot \left(-\frac{1}{x^2}\right) = 2x\sin\frac{1}{x} - \cos\frac{1}{x}$$.

We look at the limit:

$$\lim_{x \to 0} f'(x) = \lim_{x \to 0}\left(2x\sin\frac{1}{x} - \cos\frac{1}{x}\right)$$.

The first term tends to 0, but $$\cos(1/x)$$ oscillates between $$-1$$ and $$1$$ as $$x \to 0$$, so this limit does not exist.

Hence, the derivative $$f'$$ is not continuous at $$x = 0$$.

In conclusion, $$f$$ is continuous and differentiable at $$x = 0$$, but $$f'$$ is not continuous there. The correct choice is Option 2: $$f$$ is continuous but $$f'$$ is not continuous.

The given domain is $$0 \le x \le 2$$. The value of $$[x]$$ changes at the integer points $$x = 1$$ and $$x = 2$$.

Interval 1: $$0 \le x < 1 \implies [x] = 0$$

$$f(x) = \max\{1 + x + 0, \, 2 + x, \, x + 2(0)\}$$

$$f(x) = \max\{1 + x, \, 2 + x, \, x\} = 2 + x$$

Interval 2: $$1 \le x < 2 \implies [x] = 1$$

$$f(x) = \max\{1 + x + 1, \, 2 + x, \, x + 2(1)\}$$

$$f(x) = \max\{2 + x, \, 2 + x, \, x + 2\} = 2 + x$$

At the boundary point: $$x = 2 \implies [x] = 2$$

$$f(x) = \max\{1 + 2 + 2, \, 2 + 2, \, 2 + 2(2)\}$$

$$f(x) = \max\{5, \, 4, \, 6\} = 6$$

For all $$0 \le x < 2$$, the function simplifies identically to $$2 + x$$:

$$f(x) = \begin{cases} 2 + x, & 0 \le x < 2 \\ 6, & x = 2 \end{cases}$$

Since $$f(x) = 2+x$$ is a linear polynomial, it is continuous everywhere inside $$(0, 2)$$. We only need to check the boundary transition at $$x = 2$$:

$$\lim_{x \to 2^-} f(x) = \lim_{x \to 2^-} (2 + x) = 4$$

$$f(2) = 6$$

Since $$\lim_{x \to 2^-} f(x) \neq f(2)$$, the function is discontinuous at exactly one point ($$x = 2$$) in the closed interval $$[0,2]$$.

$$m = 1 \quad (\text{at } x = 2)$$

Within $$(0, 2)$$, $$f(x) = 2 + x$$. 

$$f'(x) = 1$$

Since the derivative exists and is constant for all values inside $$(0, 2)$$, there are no points of non-differentiability in this open interval:

$$n = 0$$

$$\text{Value} = (1 + 0)^2 + 2 = 1 + 2 = 3$$

We are given a piecewise function:

$$f(x) = \begin{cases} 3x^2 + k\sqrt{x + 1}, & 0 < x < 1 \\ mx^2 + k^2, & x \geq 1 \end{cases}$$

where $$k$$ and $$m$$ are positive real numbers, and $$f(x)$$ is differentiable for all $$x > 0$$.

For $$f$$ to be differentiable at $$x = 1$$, it must first be continuous there. Equating the left-hand and right-hand limits:

$$3(1)^2 + k\sqrt{1 + 1} = m(1)^2 + k^2$$

$$3 + k\sqrt{2} = m + k^2 \quad \cdots (i)$$

The derivatives of each piece are:

For $$0 < x < 1$$: $$f'(x) = 6x + \dfrac{k}{2\sqrt{x+1}}$$

For $$x \geq 1$$: $$f'(x) = 2mx$$

Equating derivatives at $$x = 1$$:

$$6 + \dfrac{k}{2\sqrt{2}} = 2m \quad \cdots (ii)$$

From equation (ii): $$m = 3 + \dfrac{k}{4\sqrt{2}}$$

Substituting into equation (i):

$$3 + k\sqrt{2} = 3 + \dfrac{k}{4\sqrt{2}} + k^2$$

$$k\sqrt{2} - \dfrac{k}{4\sqrt{2}} = k^2$$

$$k\left(\sqrt{2} - \dfrac{1}{4\sqrt{2}}\right) = k^2$$

Since $$k > 0$$, we divide both sides by $$k$$:

$$k = \sqrt{2} - \dfrac{1}{4\sqrt{2}} = \dfrac{8 - 1}{4\sqrt{2}} = \dfrac{7}{4\sqrt{2}} = \dfrac{7\sqrt{2}}{8}$$

Then from (ii): $$2m = 6 + \dfrac{7\sqrt{2}}{8 \cdot 2\sqrt{2}} = 6 + \dfrac{7}{16} = \dfrac{103}{16}$$

$$m = \dfrac{103}{32}$$

Since $$8 \geq 1$$, we use $$f'(x) = 2mx$$:

$$f'(8) = 2 \cdot \dfrac{103}{32} \cdot 8 = \dfrac{103}{2}$$

Since $$0 < \dfrac{1}{8} < 1$$, we use $$f'(x) = 6x + \dfrac{k}{2\sqrt{x+1}}$$:

$$f'\!\left(\dfrac{1}{8}\right) = \dfrac{3}{4} + \dfrac{\frac{7\sqrt{2}}{8}}{2\sqrt{\frac{9}{8}}} = \dfrac{3}{4} + \dfrac{\frac{7\sqrt{2}}{8}}{\frac{3}{\sqrt{2}}} = \dfrac{3}{4} + \dfrac{7\sqrt{2} \cdot \sqrt{2}}{8 \cdot 3} = \dfrac{3}{4} + \dfrac{7}{12} = \dfrac{4}{3}$$

$$\dfrac{8f'(8)}{f'\!\left(\dfrac{1}{8}\right)} = \dfrac{8 \cdot \dfrac{103}{2}}{\dfrac{4}{3}} = \dfrac{412}{\dfrac{4}{3}} = 412 \times \dfrac{3}{4} = \boxed{309}$$

Given: $$f(x) = [a + 13\sin x]$$ for $$x \in (0, \pi)$$, where $$[t]$$ denotes the greatest integer function and $$a \in \mathbb{Z}$$.

Since $$\sin x > 0$$ for $$x \in (0, \pi)$$, we have $$|sin x| = \sin x$$.

The function $$g(x) = a + 13\sin x$$ ranges from slightly above $$a$$ (near $$x = 0, \pi$$) to $$a + 13$$ (at $$x = \pi/2$$).

The floor function $$[g(x)]$$ is not differentiable whenever $$g(x)$$ passes through an integer value. Since $$a$$ is an integer, the integer values that $$g(x)$$ passes through are $$a+1, a+2, \ldots, a+12$$ (going up and coming down) and $$a+13$$ (at the peak).

For each integer $$a+k$$ where $$k = 1, 2, \ldots, 12$$: the function $$g(x)$$ crosses this value twice (once while increasing, once while decreasing), giving 2 non-differentiable points each.

For $$k = 13$$: $$g(x) = a+13$$ only at $$x = \pi/2$$ (the maximum), giving 1 non-differentiable point.

Total non-differentiable points = $$12 \times 2 + 1 = 25$$.

The answer is 25.

We need to find the number of points of discontinuity of $$f(x) = |[x]| + \sqrt{x - [x]}$$ in the interval $$(-2, 1)$$, where $$[x]$$ denotes the greatest integer function.

Note that $$x - [x] = \{x\}$$ is the fractional part function, which satisfies $$0 \leq \{x\} < 1$$. So $$f(x) = |[x]| + \sqrt{\{x\}}$$.

Let us analyze $$f(x)$$ on each sub-interval:

For $$x \in (-2, -1)$$: $$[x] = -2$$, so $$f(x) = |-2| + \sqrt{x - (-2)} = 2 + \sqrt{x + 2}$$.

For $$x \in [-1, 0)$$: $$[x] = -1$$, so $$f(x) = |-1| + \sqrt{x - (-1)} = 1 + \sqrt{x + 1}$$.

For $$x \in [0, 1)$$: $$[x] = 0$$, so $$f(x) = |0| + \sqrt{x - 0} = \sqrt{x}$$.

Checking continuity at $$x = -1$$:

Left-hand limit: $$\lim_{x \to -1^-} f(x) = 2 + \sqrt{-1 + 2} = 2 + 1 = 3$$.

Value at $$x = -1$$: $$f(-1) = 1 + \sqrt{-1 + 1} = 1 + 0 = 1$$.

Since $$3 \neq 1$$, $$f$$ is discontinuous at $$x = -1$$.

Checking continuity at $$x = 0$$:

Left-hand limit: $$\lim_{x \to 0^-} f(x) = 1 + \sqrt{0 + 1} = 1 + 1 = 2$$.

Value at $$x = 0$$: $$f(0) = \sqrt{0} = 0$$.

Since $$2 \neq 0$$, $$f$$ is discontinuous at $$x = 0$$.

Within each sub-interval $$(-2, -1)$$, $$(-1, 0)$$, and $$(0, 1)$$, the function is continuous (being a sum of a constant and a continuous radical function).

Therefore, the number of points of discontinuity in $$(-2, 1)$$ is $$\boxed{2}$$.

To solve for the number of points where $$y = |f(x)|$$ is not continuous ($$m$$) and not differentiable ($$n$$) on the interval $$(-2, 2)$$, we break down the function $$f(x)$$ based on the greatest integer function $$[x]$$.

1. Define $$f(x)$$ Piecewise

• For $$x \in (-2, -1)$$: $$[x] = -2 \implies f(x) = -2x$$
• For $$x \in [-1, 0)$$: $$[x] = -1 \implies f(x) = -x$$
• For $$x \in [0, 1)$$: $$[x] = 0 \implies f(x) = (x-1)(0) = 0$$
• For $$x \in [1, 2)$$: $$[x] = 1 \implies f(x) = (x-1)(1) = x-1$$
• At $$x = 2$$: $$[x] = 2 \implies f(x) = (2-1)(2) = 2$$

2. Analyze $$|f(x)|$$ for Continuity ($$m$$)

We check the points where the definition changes: $$x = -1, 0, 1$$.

• At $$x = -1$$: $$\lim_{x \to -1^-} |-2x| = 2$$ and $$\lim_{x \to -1^+} |-x| = 1$$. Discontinuous.
• At $$x = 0$$: $$\lim_{x \to 0^-} |-x| = 0$$ and $$\lim_{x \to 0^+} |0| = 0$$. Continuous.
• At $$x = 1$$: $$\lim_{x \to 1^-} |0| = 0$$ and $$\lim_{x \to 1^+} |x-1| = 0$$. Continuous.

So, $$m = 1$$ (at $$x = -1$$).

3. Analyze $$|f(x)|$$ for Differentiability ($$n$$)

A function is not differentiable if it is discontinuous or has a "sharp corner" (LHD $$\neq$$ RHD).

• At $$x = -1$$: Discontinuous, so not differentiable.
• At $$x = 0$$: * LHD: $$\frac{d}{dx}|-x| = \frac{d}{dx}(x) = 1$$ (since $$x$$ is negative approaching 0)
• RHD: $$\frac{d}{dx}|0| = 0$$.
• LHD $$\neq$$ RHD, so not differentiable.
• At $$x = 1$$:
• LHD: $$\frac{d}{dx}|0| = 0$$
• RHD: $$\frac{d}{dx}|x-1| = 1$$
• LHD $$\neq$$ RHD, so not differentiable.

So, $$n = 3$$ (at $$x = -1, 0, 1$$).

4. Final Calculation

$$m + n = 1 + 3 = \mathbf{4}$$

We have to find $$\displaystyle\lim_{x\to\alpha^{+}} f(g(x))$$ where

$$f(x)=\sin\!\left(\frac{\pi x}{12}\right), \qquad g(x)=\frac{2\ln\!\bigl(\sqrt{x}-\sqrt{\alpha}\bigr)}{\ln\!\bigl(e^{\sqrt{x}}-e^{\sqrt{\alpha}}\bigr)}, \qquad \alpha \gt 0.$$

Step 1 : Rewrite the limit of $$g(x)$$ as $$x\to\alpha^{+}$$.

Set $$h=\sqrt{x}-\sqrt{\alpha}, \qquad h\gt 0$$ when $$x\to\alpha^{+}.$$ Then $$\sqrt{x}=\sqrt{\alpha}+h \;\;\Longrightarrow\;\; x=(\sqrt{\alpha}+h)^{2}.$$ Consequently $$h\to0^{+}$$ is equivalent to $$x\to\alpha^{+}.$$

Step 2 : Express numerator and denominator of $$g(x)$$ in terms of $$h$$.

Numerator:

$$2\ln\!\bigl(\sqrt{x}-\sqrt{\alpha}\bigr)=2\ln h.$$

Denominator:

$$\ln\!\bigl(e^{\sqrt{x}}-e^{\sqrt{\alpha}}\bigr) =\ln\!\Bigl(e^{\sqrt{\alpha}+h}-e^{\sqrt{\alpha}}\Bigr) =\ln\!\Bigl(e^{\sqrt{\alpha}}\bigl(e^{h}-1\bigr)\Bigr)$$

$$=\ln\!\bigl(e^{\sqrt{\alpha}}\bigr)+\ln\!\bigl(e^{h}-1\bigr) =\sqrt{\alpha}+\ln\!\bigl(e^{h}-1\bigr).$$

Step 3 : Use the first-order expansion of $$e^{h}-1$$ for small $$h$$.

For $$h\to0^{+},\;\; e^{h}-1=h+\dfrac{h^{2}}{2}+O(h^{3}).$$ Hence

$$\ln\!\bigl(e^{h}-1\bigr) =\ln h+\ln\!\Bigl(1+\dfrac{h}{2}+O(h^{2})\Bigr) =\ln h+O(h).$$

Therefore

$$\text{Denominator}= \sqrt{\alpha}+\ln h+O(h).$$

Step 4 : Evaluate the limit of $$g(x)$$.

Combine the results:

$$g(x)=\frac{2\ln h}{\ln h+\sqrt{\alpha}+O(h)} =\frac{2}{1+\dfrac{\sqrt{\alpha}+O(h)}{\ln h}}.$$

As $$h\to0^{+},\; \ln h\to-\infty\;$$ so $$\dfrac{\sqrt{\alpha}+O(h)}{\ln h}\to0.$$ Thus

$$\lim_{h\to0^{+}} g(x)=2.$$

Step 5 : Apply $$f(x)=\sin\!\left(\dfrac{\pi x}{12}\right)$$ to this limit.

$$\lim_{x\to\alpha^{+}} f\!\bigl(g(x)\bigr) =\sin\!\left(\frac{\pi}{12}\times\lim_{x\to\alpha^{+}} g(x)\right) =\sin\!\left(\frac{\pi}{12}\times2\right) =\sin\!\left(\frac{\pi}{6}\right) =\frac12.$$

Therefore the required limit equals 0.50.

Let

$$N(x)=e^{x^{3}}-\left(1-x^{3}\right)^{1/3}+\bigl((1-x^{2})^{1/2}-1\bigr)\sin x,$$
$$D(x)=x\sin^{2}x.$$

We need $$\beta=\displaystyle\lim_{x\to 0}\dfrac{N(x)}{D(x)}.$$

Step 1 : Expand every term about $$x=0$$

Maclaurin series that will be used:

• $$e^{t}=1+t+\dfrac{t^{2}}{2}+\dots$$
• $$(1+u)^{n}=1+nu+\dfrac{n(n-1)}{2}u^{2}+\dots$$
• $$\sin x = x-\dfrac{x^{3}}{6}+\dfrac{x^{5}}{120}+\dots$$

(i) $$e^{x^{3}} = 1+x^{3}+\dfrac{x^{6}}{2}+O(x^{9}).$$

(ii) $$(1-x^{3})^{1/3}=1+\dfrac{1}{3}(-x^{3})+\dfrac{1/3(-2/3)}{2}(-x^{3})^{2}+O(x^{9}) =1-\dfrac{x^{3}}{3}-\dfrac{x^{6}}{9}+O(x^{9}).$$

Hence

$$e^{x^{3}}-\left(1-x^{3}\right)^{1/3} =(1+x^{3}+\tfrac{x^{6}}{2})-(1-\tfrac{x^{3}}{3}-\tfrac{x^{6}}{9})+O(x^{9}) =\dfrac{4}{3}x^{3}+\dfrac{11}{18}x^{6}+O(x^{9}).$$

(iii) $$(1-x^{2})^{1/2}=1-\dfrac{x^{2}}{2}-\dfrac{x^{4}}{8}+O(x^{6}),$$
so $$(1-x^{2})^{1/2}-1=-\dfrac{x^{2}}{2}-\dfrac{x^{4}}{8}+O(x^{6}).$$

Multiply by $$\sin x$$:

$$\bigl((1-x^{2})^{1/2}-1\bigr)\sin x =\Bigl(-\dfrac{x^{2}}{2}-\dfrac{x^{4}}{8}+O(x^{6})\Bigr) \Bigl(x-\dfrac{x^{3}}{6}+\dfrac{x^{5}}{120}+O(x^{7})\Bigr).$$

Keep terms up to $$x^{5}$$ (higher-order terms will vanish upon taking the limit):

$$$ \begin{aligned} &-\dfrac{x^{2}}{2}\cdot x =-\dfrac{x^{3}}{2},\\ &-\dfrac{x^{2}}{2}\cdot\Bigl(-\dfrac{x^{3}}{6}\Bigr)=+\dfrac{x^{5}}{12},\\ &-\dfrac{x^{4}}{8}\cdot x =-\dfrac{x^{5}}{8}. \end{aligned} $$$

Adding these,

$$\bigl((1-x^{2})^{1/2}-1\bigr)\sin x =-\dfrac{x^{3}}{2}-\dfrac{x^{5}}{24}+O(x^{7}).$$

(iv) Combine parts (i)-(iii):

$$$ \begin{aligned} N(x)&=\Bigl(\dfrac{4}{3}x^{3}+\dfrac{11}{18}x^{6}\Bigr) +\Bigl(-\dfrac{x^{3}}{2}-\dfrac{x^{5}}{24}\Bigr)+O(x^{7})\\ &=\dfrac{5}{6}x^{3}-\dfrac{x^{5}}{24}+\dfrac{11}{18}x^{6}+O(x^{7}). \end{aligned} $$$

(v) Now expand the denominator:

$$\sin x = x-\dfrac{x^{3}}{6}+\dfrac{x^{5}}{120}+O(x^{7}),$$

so

$$\sin^{2}x =\bigl(x-\dfrac{x^{3}}{6}+\dfrac{x^{5}}{120}\bigr)^{2} =x^{2}-\dfrac{x^{4}}{3}+\dfrac{2x^{6}}{45}+O(x^{8}).$$

Therefore

$$D(x)=x\sin^{2}x =x^{3}-\dfrac{x^{5}}{3}+\dfrac{2x^{7}}{45}+O(x^{9}).$$

Step 2 : Form the quotient

Write both series factored by $$x^{3}$$:

$$N(x)=x^{3}\Bigl(\dfrac{5}{6}-\dfrac{x^{2}}{24}+\dfrac{11x^{3}}{18}+O(x^{4})\Bigr),$$

$$D(x)=x^{3}\Bigl(1-\dfrac{x^{2}}{3}+\dfrac{2x^{4}}{45}+O(x^{6})\Bigr).$$

Hence

$$\dfrac{N(x)}{D(x)} =\dfrac{\dfrac{5}{6}-\dfrac{x^{2}}{24}+O(x^{3})} {1-\dfrac{x^{2}}{3}+O(x^{4})}.$$

Using $$\dfrac{1}{1-z}=1+z+O(z^{2})$$ for small $$z$$,

$$$ \begin{aligned} \frac{N(x)}{D(x)} &=\Bigl(\dfrac{5}{6}-\dfrac{x^{2}}{24}+O(x^{3})\Bigr) \Bigl(1+\dfrac{x^{2}}{3}+O(x^{4})\Bigr)\\[4pt] &=\dfrac{5}{6}+O(x^{2}). \end{aligned} $$$

Step 3 : Take the limit

As $$x\to 0$$, the higher-order terms vanish, giving

$$\beta=\dfrac{5}{6}.$$

Therefore

$$6\beta = 6\left(\dfrac{5}{6}\right)=5.$$

Final Answer: 5

We are given $$f(x) = \dfrac{x}{(1+x)^{1/x}}$$ for $$x > 0$$ and $$f(0) = e$$.

To check continuity at $$x = 0$$, we evaluate $$\displaystyle\lim_{x \to 0^+} f(x)$$.

We know the standard limit $$\displaystyle\lim_{x \to 0} (1+x)^{1/x} = e$$.

As $$x \to 0^+$$, the numerator $$x \to 0$$ and the denominator $$(1+x)^{1/x} \to e$$.

Therefore $$\displaystyle\lim_{x \to 0^+} f(x) = \dfrac{0}{e} = 0$$.

But $$f(0) = e \neq 0$$. Since the limit does not equal the function value, $$f$$ is not continuous at $$x = 0$$.

The correct answer is Option D.

We have $$f(x) = \lim_{n \to \infty} \frac{\cos(2\pi x) - x^{2n}\sin(x-1)}{1 + x^{2n+1} - x^{2n}}$$.

To evaluate this limit, we need to consider different cases based on the value of $$|x|$$.

Case 1: $$|x| < 1$$. Here $$x^{2n} \to 0$$ and $$x^{2n+1} \to 0$$ as $$n \to \infty$$. So $$f(x) = \frac{\cos(2\pi x) - 0}{1 + 0 - 0} = \cos(2\pi x)$$.

Case 2: $$|x| > 1$$. We divide numerator and denominator by $$x^{2n}$$:

Case 3: $$x = 1$$. Then $$x^{2n} = 1$$ and $$x^{2n+1} = 1$$. So $$f(1) = \frac{\cos(2\pi) - \sin(0)}{1 + 1 - 1} = \frac{1 - 0}{1} = 1$$.

Case 4: $$x = -1$$. Then $$x^{2n} = (-1)^{2n} = 1$$ and $$x^{2n+1} = (-1)^{2n+1} = -1$$. So $$f(-1) = \frac{\cos(-2\pi) - \sin(-2)}{1 + (-1) - 1} = \frac{1 - \sin(-2)}{-1} = \frac{1 + \sin 2}{-1} = -(1 + \sin 2)$$.

Now let us check continuity at the critical points $$x = 1$$ and $$x = -1$$.

At $$x = 1$$: From Case 1 (as $$x \to 1^-$$): $$\cos(2\pi \cdot 1) = 1$$. From Case 2 (as $$x \to 1^+$$): $$\frac{-\sin(x-1)}{x-1} \to -1$$ (since $$\frac{\sin(x-1)}{x-1} \to 1$$). The function value is $$f(1) = 1$$. Since the left limit is 1 but the right limit is $$-1$$, the function is discontinuous at $$x = 1$$.

At $$x = -1$$: From Case 1 (as $$x \to -1^+$$): $$\cos(2\pi(-1)) = \cos(-2\pi) = 1$$. From Case 2 (as $$x \to -1^-$$): $$\frac{-\sin(-1-1)}{-1-1} = \frac{-\sin(-2)}{-2} = \frac{\sin 2}{-2} = -\frac{\sin 2}{2}$$. The function value is $$f(-1) = -(1 + \sin 2)$$. The left limit is $$-\frac{\sin 2}{2}$$ and the right limit is $$1$$, neither of which equals $$-(1 + \sin 2)$$. So the function is discontinuous at $$x = -1$$.

For all other points, the function is continuous (being composed of continuous functions in each region, with the regions being open intervals).

Therefore $$f$$ is continuous for all $$x \in \mathbb{R} - \{-1, 1\}$$.

Hence, the correct answer is Option 2.

Given,

$$f(x)= \begin{cases} \dfrac{\sin(x-|x|)}{x-|x|}, & x\in(-2,-1)\\ \max(2x,3[|x|]), &|x|<1\\ 1, & \text{otherwise} \end{cases}$$

First simplify the function in different intervals.

For $$x\in(-2,-1),$$

$$|x|=-x$$

Hence,

$$x-|x|=x-(-x)=2x$$

Therefore,

$$f(x)=\frac{\sin2x}{2x},\qquad x\in(-2,-1)$$

Now for $$|x|<1,$$

$$0\le |x|<1$$

Hence,

$$[|x|]=0$$

Therefore,

$$3[|x|]=0$$

So,

$$f(x)=\max(2x,0)$$

Thus,

$$f(x)=\begin{cases}0, & -1<x<0\\ 2x, & 0\le x<1 \end{cases}$$

Now check continuity at possible critical points.

At $$x=-2,$$

$$f(-2)=1$$

Also,

$$f(-2^+)=\lim_{x\to-2^+}\frac{\sin2x}{2x}=\frac{\sin(-4)}{-4}\neq1$$

Hence, $$f$$ is discontinuous at $$x=-2$$.

At $$x=-1,$$

$$f(-1)=1$$

Also,

$$f(-1^-)=\frac{\sin(-2)}{-2},\qquad f(-1^+)=0$$

Since left and right limits are unequal, $$f$$ is discontinuous at $$x=-1$$.

At $$x=0,$$

$$f(0^-)=0,\qquad f(0^+)=0,\qquad f(0)=0$$

Hence, $$f$$ is continuous at $$x=0$$.

At $$x=1,$$

$$f(1^-)=2,\qquad f(1)=1$$

Hence, $$f$$ is discontinuous at $$x=1$$.

Therefore, the number of discontinuity points is

$$m=3$$

Now check differentiability.

At $$x=-2,-1,1,$$ the function is discontinuous, so it is not differentiable.

At $$x=0,$$

$$f(x)=0\quad(-1<x<0)$$

and

$$f(x)=2x\quad(0<x<1)$$

Hence,

$$f'_-(0)=0,\qquad f'_+(0)=2$$

Since LHD and RHD are unequal, $$f$$ is not differentiable at $$x=0$$.

Therefore,

$$n=4$$

Hence, the ordered pair is

$$\boxed{(3,4)}$$.

We need to find $$k$$ such that the given piecewise function is continuous at $$x = 0$$, i.e., $$k = \displaystyle\lim_{x \to 0} \frac{\log_e(1-x+x^2) + \log_e(1+x+x^2)}{\sec x - \cos x}$$.

Using the logarithm property $$\log a + \log b = \log(ab)$$:

$$\log_e(1-x+x^2) + \log_e(1+x+x^2) = \log_e\left((1-x+x^2)(1+x+x^2)\right)$$

Expanding the product:

$$(1-x+x^2)(1+x+x^2) = (1+x^2)^2 - x^2 = 1 + 2x^2 + x^4 - x^2 = 1 + x^2 + x^4$$

So the numerator = $$\log_e(1 + x^2 + x^4)$$.

$$\sec x - \cos x = \frac{1}{\cos x} - \cos x = \frac{1 - \cos^2 x}{\cos x} = \frac{\sin^2 x}{\cos x}$$

$$\lim_{x \to 0} \frac{\log_e(1 + x^2 + x^4)}{\dfrac{\sin^2 x}{\cos x}} = \lim_{x \to 0} \frac{\log_e(1 + x^2 + x^4) \cdot \cos x}{\sin^2 x}$$

As $$x \to 0$$, using the standard limit $$\log_e(1+u) \approx u$$ for small $$u$$:

$$\log_e(1 + x^2 + x^4) \approx x^2 + x^4 \quad (\text{since } x^2 + x^4 \to 0)$$

Also, as $$x \to 0$$: $$\sin x \approx x$$, so $$\sin^2 x \approx x^2$$, and $$\cos x \to 1$$.

Substituting these approximations:

$$\lim_{x \to 0} \frac{(x^2 + x^4) \cdot 1}{x^2} = \lim_{x \to 0} (1 + x^2) = 1$$

We can verify using L'Hopital's rule. As $$x \to 0$$, both numerator and denominator approach 0 (it is a $$\frac{0}{0}$$ form since $$\log_e(1) = 0$$ and $$\sec 0 - \cos 0 = 0$$).

For continuity at $$x = 0$$, we need $$k = 1$$.

Therefore, the correct answer is Option A: 1.

We analyze the piecewise function for continuity at the boundary points $$x = 0, 1, 2$$. For $$x < 0$$ we have $$f(x) = [e^x]$$, and since $$0 < e^x < 1$$ for $$x < 0$$, $$[e^x] = 0$$. For $$0 \le x < 1$$, $$f(x) = ae^x + [x-1]$$, and since $$x - 1 \in [-1, 0)$$, $$[x-1] = -1$$, so $$f(x) = ae^x - 1$$. For $$1 \le x < 2$$, $$f(x) = b + [\sin(\pi x)]$$; at $$x = 1$$, $$\sin(\pi) = 0$$ gives $$[\sin(\pi)] = 0$$ and $$f(1) = b$$, while for $$x \in (1, 2)$$, $$\sin(\pi x) < 0$$ since $$\pi x \in (\pi, 2\pi)$$ and $$-1 \le \sin(\pi x) < 0$$, so $$[\sin(\pi x)] = -1$$ and $$f(x) = b - 1$$. For $$x \ge 2$$, $$f(x) = [e^{-x}] - c$$, and since $$0 < e^{-x} < 1$$ for $$x \ge 2$$, $$[e^{-x}] = 0$$, hence $$f(x) = -c$$.

The left limit at $$x \to 0^-$$ is $$\lim_{x \to 0^-} [e^x] = 0$$, and the right value is $$f(0) = a\cdot1 - 1 = a - 1$$, so continuity at $$x = 0$$ gives $$a - 1 = 0$$ and thus $$a = 1$$.

At $$x = 1$$, $$f(1) = b$$ but the right-hand limit is $$\lim_{x \to 1^+} f(x) = b - 1$$, which never equals $$b$$ for any $$b$$, so $$f$$ is always discontinuous at $$x = 1$$, making Option A false.

The left limit at $$x \to 2^-$$ is $$b - 1$$ and $$f(2) = -c$$, so continuity at $$x = 2$$ requires $$b - 1 = -c$$, giving $$c = 1 - b$$.

For $$f$$ to be discontinuous at exactly one point (namely $$x = 1$$), it must be continuous at $$x = 0$$ and $$x = 2$$, so $$a = 1$$ and $$c = 1 - b$$. Since $$b$$ can be any real number, we have $$a + b + c = 1 + b + (1 - b) = 2 \neq 1$$.

Option B is false, and Option C is true. Therefore, the correct answer is Option C.

We have $$f(x) = |x - 1|\cos|x - 2|\sin|x - 1| + (x - 3)|x^2 - 5x + 4|$$. We note that $$x^2 - 5x + 4 = (x - 1)(x - 4)$$, so the critical points to examine for differentiability are $$x = 1, 2, 3,$$ and $$4$$.

At $$x = 2$$: Near $$x = 2$$, we have $$|x - 1| = x - 1$$ (smooth) and $$\sin|x - 1| = \sin(x - 1)$$ (smooth). Also, $$\cos|x - 2| = \cos(|x - 2|)$$, and since cosine is an even function, $$\cos|x - 2| = \cos(x - 2)$$, which is differentiable. For the second term, $$x^2 - 5x + 4 < 0$$ near $$x = 2$$, so $$|x^2 - 5x + 4| = -(x^2 - 5x + 4)$$, a polynomial. Hence $$f$$ is differentiable at $$x = 2$$.

At $$x = 3$$: Near $$x = 3$$, $$|x - 1| = x - 1$$ and $$|x - 2| = x - 2$$ are both smooth. Also $$x^2 - 5x + 4 < 0$$ near $$x = 3$$ (since $$9 - 15 + 4 = -2$$), so $$|x^2 - 5x + 4| = -(x^2 - 5x + 4)$$, again a polynomial. Hence $$f$$ is differentiable at $$x = 3$$.

At $$x = 1$$: The first term is $$|x - 1|\cos|x - 2|\sin|x - 1|$$. Near $$x = 1$$, $$|x - 1|\sin|x - 1| \approx (x - 1)^2$$ (since $$\sin|x-1|/|x-1| \to 1$$), which is smooth with derivative 0 at $$x = 1$$. So the first term is differentiable at $$x = 1$$.

The second term is $$(x - 3)|(x - 1)(x - 4)| = (x - 3)(4 - x)|x - 1|$$ near $$x = 1$$ (since $$x - 4 < 0$$). For $$x > 1$$: this equals $$(x - 3)(4 - x)(x - 1)$$, with derivative at $$x = 1$$: evaluating from the expansion, we get $$(-2)(3)(1) = -6$$... more precisely, we compute the derivative of $$g(x) = (x-3)(4-x)(x-1)$$ at $$x = 1$$: $$g'(x)$$ at $$x = 1$$ equals $$(4-x)(x-1) + (x-3)(-(x-1)) + (x-3)(4-x)$$ evaluated at $$x = 1$$, giving $$0 + 0 + (-2)(3) = -6$$.

For $$x < 1$$: this equals $$(x - 3)(4 - x)(1 - x)$$, and by the same method the derivative at $$x = 1$$ is $$0 + 0 + (-2)(3)(-1) = 6$$.

Since the left derivative ($$6$$) differs from the right derivative ($$-6$$), $$f$$ is not differentiable at $$x = 1$$.

At $$x = 4$$: The first term is differentiable ($$|x - 1|$$ and $$|x - 2|$$ are smooth near $$x = 4$$). The second term is $$(x - 3)(x - 1)|x - 4|$$.

For $$x > 4$$: $$(x - 3)(x - 1)(x - 4)$$. The derivative at $$x = 4$$ is: expanding as $$h(x) = (x^2 - 4x + 3)(x - 4)$$, we get $$h'(x) = (2x - 4)(x - 4) + (x^2 - 4x + 3)$$, so $$h'(4) = 0 + 3 = 3$$.

For $$x < 4$$: $$(x - 3)(x - 1)(4 - x)$$. The derivative at $$x = 4$$ is: expanding as $$h(x) = (x^2 - 4x + 3)(4 - x) = -x^3 + 8x^2 - 19x + 12$$, we get $$h'(x) = -3x^2 + 16x - 19$$, so $$h'(4) = -48 + 64 - 19 = -3$$.

Since the left derivative ($$-3$$) differs from the right derivative ($$3$$), $$f$$ is not differentiable at $$x = 4$$.

In total, $$f$$ is not differentiable at exactly 2 points: $$x = 1$$ and $$x = 4$$.

Hence, the correct answer is Option B.

Given,

$$f(x)=\frac{\sqrt[7]{p(729+x)}-3}{\sqrt[3]{729+qx}-9}$$

For continuity at

$$x=0,$$

the limit must exist.

Substituting $$x=0$$ in denominator,

$$\sqrt[3]{729}-9=9-9=0$$

Hence numerator must also become zero.

Therefore,

$$\sqrt[7]{p(729)}-3=0$$

Since

$$729=3^6,$$

$$\sqrt[7]{3^6p}=3$$

$$3^6p=3^7$$

$$p=3$$

Now evaluate

$$f(0)=\lim_{x\to0}\frac{\sqrt[7]{3(729+x)}-3}{\sqrt[3]{729+qx}-9}$$

Using L’Hôpital’s Rule,

$$f(0)=\lim_{x\to0}\frac{\frac{1}{7}[3(729+x)]^{-6/7}\cdot3}{\frac13(729+qx)^{-2/3}\cdot q}$$

Substituting $$x=0,$$

$$f(0)=\frac{\frac{3}{7(3^7)^{6/7}}}{\frac{q}{3(3^6)^{2/3}}}$$

$$=\frac{\frac{3}{7\cdot3^6}}{\frac{q}{3\cdot3^4}}$$

$$=\frac{1}{7q}$$

Hence,

$$7qf(0)=1$$

Since

$$p=3,$$

$$p^2=9$$

Multiplying by $$9,$$

$$63qf(0)=9=p^2$$

Therefore,

$$63qf(0)-p^2=0$$

Hence, the correct relation is

$$\boxed{63qf(0)-p^2=0}$$.

We have $$f(x) = \begin{cases} x + a, & x \le 0 \\ |x - 4|, & x > 0 \end{cases}$$ and $$g(x) = \begin{cases} x + 1, & x < 0 \\ (x-4)^2 + b, & x \ge 0 \end{cases}$$

To ensure continuity at $$x = 0$$, for $$f$$ the left limit is $$0 + a = a$$ and the right limit is $$|0 - 4| = 4$$, so $$a = 4$$. Substituting this into $$g$$, the left limit is $$0 + 1 = 1$$ and the right value is $$(0-4)^2 + b = 16 + b$$, giving $$b = -15$$.

Next, since $$2 > 0$$, we have $$f(2) = |2 - 4| = 2$$ and then $$g(f(2)) = g(2) = (2 - 4)^2 + (-15) = 4 - 15 = -11$$ (since $$2 \ge 0$$).

Then, for $$(f \circ g)(-2)$$, we compute $$g(-2) = -2 + 1 = -1$$ (since $$-2 < 0$$) and $$f(g(-2)) = f(-1) = -1 + 4 = 3$$ (since $$-1 \le 0$$).

From this, $$(g \circ f)(2) + (f \circ g)(-2) = -11 + 3 = -8$$.

Therefore, the correct answer is Option D: $$-8$$.

Given:

$$f(x) = \begin{cases} [x], & x < 0 \\ |1 - x|, & x \geq 0 \end{cases}$$

$$g(x) = \begin{cases} e^x - x, & x < 0 \\ (x - 1)^2 - 1, & x \geq 0 \end{cases}$$

where $$[x]$$ is the greatest integer function.

Analyze $$g(x)$$ on different intervals:

• For $$x < 0$$: $$g(x) = e^x - x$$. Since $$g'(x) = e^x - 1 < 0$$, $$g$$ is decreasing. As $$x \to -\infty$$, $$g \to +\infty$$; at $$x = 0^-$$, $$g \to 1$$. So $$g(x) > 1$$ for all $$x < 0$$.
• For $$x \geq 0$$: $$g(x) = (x-1)^2 - 1 = x^2 - 2x = x(x - 2)$$. Minimum at $$x = 1$$: $$g(1) = -1$$. Also $$g(0) = 0$$ and $$g(2) = 0$$.

Compute $$f(g(x))$$ on each interval:

For $$x < 0$$: $$g(x) > 1 \geq 0$$, so $$f(g(x)) = |1 - g(x)| = g(x) - 1 = e^x - x - 1$$. This is continuous on $$(-\infty, 0)$$.

For $$x \geq 0$$: We need to split based on the sign of $$g(x)$$:

• $$g(x) < 0$$ for $$x \in (0, 2)$$: Here $$g(x) \in [-1, 0)$$, so $$f(g(x)) = [g(x)]$$. Since $$g(x) \in [-1, 0)$$, we get $$[g(x)] = -1$$. So $$f(g(x)) = -1$$ on $$(0, 2)$$.
• $$g(x) = 0$$ at $$x = 0$$ and $$x = 2$$: $$f(0) = |1 - 0| = 1$$.
• $$g(x) > 0$$ for $$x > 2$$: $$f(g(x)) = |1 - g(x)| = |1 - x^2 + 2x|$$.

Check continuity at critical points:

At $$x = 0$$:

• Left limit: $$\lim_{x \to 0^-} (e^x - x - 1) = 1 - 0 - 1 = 0$$
• Right limit: $$\lim_{x \to 0^+} [g(x)] = [g(0^+)]$$. For $$x$$ slightly greater than 0, $$g(x) = x(x-2) \approx -2x < 0$$, so $$[g(x)] = -1$$.
• Value: $$f(g(0)) = f(0) = |1 - 0| = 1$$
• Left limit $$= 0$$, right limit $$= -1$$, value $$= 1$$: Discontinuous $$\boldsymbol{\times}$$

At $$x = 2$$:

• Left limit: $$\lim_{x \to 2^-} (-1) = -1$$
• Right limit: $$\lim_{x \to 2^+} |1 - x^2 + 2x| = |1 - 4 + 4| = 1$$
• Value: $$f(g(2)) = f(0) = 1$$
• Left limit $$= -1 \neq 1$$: Discontinuous $$\boldsymbol{\times}$$

For $$x > 2$$: $$f(g(x)) = |1 - x^2 + 2x| = |-(x^2 - 2x - 1)| = |-(x - 1)^2 + 2|$$

This equals $$2 - (x-1)^2$$ when $$(x-1)^2 < 2$$, i.e., $$x < 1 + \sqrt{2} \approx 2.414$$, and $$(x-1)^2 - 2$$ otherwise. At $$x = 1 + \sqrt{2}$$, the expression inside the absolute value is 0, and the function is continuous.

No other points of discontinuity exist (the function on $$(-\infty, 0)$$ and $$(0, 2)$$ and $$(2, \infty)$$ are each continuous within their intervals).

Therefore, $$f \circ g$$ is discontinuous at exactly two points: $$x = 0$$ and $$x = 2$$.

The correct answer is Option B: two points.

Given,

$$f(x)=\min\{1,1+x\sin x\},\qquad 0\le x\le2\pi$$

Now,

$$f(x)=1$$

when

$$1\le1+x\sin x$$

$$x\sin x\ge0$$

Since

$$x\ge0$$

for $$0\le x\le2\pi$$ the sign depends on $$\sin x$$.

Thus,

$$f(x)=1\quad \text{for}\quad 0\le x\le\pi$$

and

$$f(x)=1+x\sin x\quad \text{for}\quad \pi<x<2\pi$$

Also,

$$f(2\pi)=1$$

Now, at $$x=\pi$$

$$\lim_{x\to\pi^-}f(x)=1$$

and

$$\lim_{x\to\pi^+}f(x)=1+\pi\sin\pi=1$$

Hence, $$f$$ is continuous at $$x=\pi$$.

Also, $$f$$ is continuous at $$x=2\pi$$.

Therefore, $$n=0$$

Now, checking differentiability at $$x=\pi$$,

Left derivative: $$f'_-(\pi)=0$$

Right derivative: $$f'_+(\pi)=\sin\pi+\pi\cos\pi=-\pi$$

Since,

$$f'_-(\pi)\ne f'_+(\pi)$$

the function is not differentiable at $$x=\pi$$.

Hence, $$m=1$$

Therefore, the ordered pair is $$\boxed{(1,0)}$$.

We need the function $$f(x) = \begin{cases} \dfrac{\log_e(1+5x) - \log_e(1+\alpha x)}{x} & \text{if } x \neq 0 \\ 10 & \text{if } x = 0 \end{cases}$$ to be continuous at $$x = 0$$.

For continuity, we need $$\displaystyle\lim_{x \to 0} f(x) = f(0) = 10$$. We compute the limit using the standard result $$\displaystyle\lim_{x \to 0} \dfrac{\log_e(1+kx)}{x} = k$$.

We have $$\displaystyle\lim_{x \to 0} \dfrac{\log_e(1+5x) - \log_e(1+\alpha x)}{x} = \lim_{x \to 0} \dfrac{\log_e(1+5x)}{x} - \lim_{x \to 0} \dfrac{\log_e(1+\alpha x)}{x} = 5 - \alpha$$.

Setting $$5 - \alpha = 10$$, we get $$\alpha = -5$$.

Hence, the correct answer is Option D: $$-5$$.

Given,

$$f(x)= \begin{cases} |2x^2-3x-7|, & x\le-1\\ [4x^2-1], & -1<x<1\\ |x+1|+|x-2|, & x\ge1\end{cases}$$

For $$x\le-1$$ and $$x\ge1,$$ the functions are continuous.

So, discontinuities can occur only:

- inside $$(-1,1)$$ due to GIF
- at $$x=-1,1$$

Now,

$$f(x)=[4x^2-1],\qquad -1<x<1$$

Since

$$-1\le4x^2-1<3$$

possible integer values are

$$-1,0,1,2$$

Case 1:

$$4x^2-1=-1\implies x=0$$

At $$x=0,$$ the GIF does not jump.

Hence, continuous at $$x=0$$.

Case 2:

$$4x^2-1=0\implies x=\pm\frac12$$

Discontinuous at both points.

Case 3:

$$4x^2-1=1\implies x=\pm\frac1{\sqrt2}$$

Discontinuous at both points.

Case 4:

$$4x^2-1=2\implies x=\pm\frac{\sqrt3}{2}$$

Discontinuous at both points.

Thus, discontinuities inside $$(-1,1)$$ are

$$x=\pm\frac12,\ \pm\frac1{\sqrt2},\ \pm\frac{\sqrt3}{2}$$

Total points $$=6$$

Now check boundary points.

At $$x=-1,$$

$$f(-1)=2,\qquad \lim_{x\to-1^-}f(x)=2,\qquad \lim_{x\to-1^+}f(x)=2$$

Hence, continuous at $$x=-1$$.

At $$x=1,$$

$$\lim_{x\to1^-}f(x)=2,\qquad f(1)=3$$

Hence, discontinuous at $$x=1$$.

Therefore, total number of discontinuity points is

$$6+1=7$$

Hence, $$\boxed{7}$$.

We have $$f(x) = [2x^2 + 1]$$ (where $$[\cdot]$$ is the greatest integer function) and $$g(x) = \begin{cases} 2x - 3, & x < 0 \\ 2x + 3, & x \geq 0 \end{cases}$$.

We need to find the number of points where $$f \circ g$$ is discontinuous in $$(-1, 1)$$.

For $$x \in (-1, 0)$$: $$g(x) = 2x - 3$$, so $$g(x) \in (-5, -3)$$. Then $$f(g(x)) = [2(2x-3)^2 + 1] = [2(4x^2 - 12x + 9) + 1] = [8x^2 - 24x + 19]$$.

As $$x$$ ranges over $$(-1, 0)$$, the expression $$h_1(x) = 8x^2 - 24x + 19$$ is a continuous function. At $$x = -1$$: $$h_1(-1) = 8 + 24 + 19 = 51$$. At $$x = 0$$: $$h_1(0) = 19$$. The minimum of $$h_1$$ on $$(-1, 0)$$ is at $$x = 0$$ (since vertex is at $$x = 3/2$$ which is outside this interval), so $$h_1$$ decreases from $$51$$ to $$19$$ on $$(-1, 0)$$.

The greatest integer function $$[h_1(x)]$$ is discontinuous whenever $$h_1(x)$$ passes through an integer. Since $$h_1$$ decreases continuously from $$51$$ to $$19$$, it passes through the integers $$50, 49, 48, \ldots, 20$$ — that is $$31$$ integer values. Each gives a point of discontinuity.

For $$x \in [0, 1)$$: $$g(x) = 2x + 3$$, so $$g(x) \in [3, 5)$$. Then $$f(g(x)) = [2(2x+3)^2 + 1] = [8x^2 + 24x + 19]$$.

Let $$h_2(x) = 8x^2 + 24x + 19$$. At $$x = 0$$: $$h_2(0) = 19$$. At $$x = 1$$: $$h_2(1) = 8 + 24 + 19 = 51$$. The function $$h_2$$ increases from $$19$$ to $$51$$ on $$[0, 1)$$, passing through integers $$20, 21, \ldots, 50$$ — that is $$31$$ integer values, each giving a discontinuity.

At $$x = 0$$, we check continuity. From the left: $$\lim_{x \to 0^-} [8x^2 - 24x + 19] = [19] = 19$$. From the right: $$f(g(0)) = [8(0) + 24(0) + 19] = [19] = 19$$. Since both sides give $$19$$, $$f \circ g$$ is continuous at $$x = 0$$. So $$x = 0$$ does not add a discontinuity.

The total number of discontinuities is $$31 + 31 = 62$$.

We have $$f(x) = 4|2x+3| + 9\!\left[x + \frac{1}{2}\right] - 12[x + 20]$$ on the open interval $$(-20, 20)$$, where $$[t]$$ denotes the greatest integer less than or equal to $$t$$.

Since 20 is an integer, $$[x + 20] = [x] + 20$$, so $$f(x) = 4|2x+3| + 9\!\left[x + \frac{1}{2}\right] - 12[x] - 240$$.

The term $$4|2x+3|$$ is continuous everywhere and differentiable at all points except $$x = -\frac{3}{2}$$, where the expression inside the absolute value changes sign.

The floor function $$[x]$$ is discontinuous (and hence not differentiable) at every integer. The floor function $$\left[x + \frac{1}{2}\right]$$ is discontinuous at every point where $$x + \frac{1}{2}$$ is an integer, i.e., at every half-integer of the form $$x = n - \frac{1}{2}$$ for integer $$n$$. These are the points $$\ldots, -\frac{3}{2}, -\frac{1}{2}, \frac{1}{2}, \frac{3}{2}, \ldots$$

The combination $$g(x) = 9\!\left[x + \frac{1}{2}\right] - 12[x]$$ is potentially not differentiable at every integer and every half-integer. At an integer $$x = n$$, the function $$[x]$$ jumps by 1 (causing a discontinuity of $$-12$$) while $$\left[x + \frac{1}{2}\right]$$ is continuous. Since the jump is $$-12 \neq 0$$, $$g$$ is discontinuous at every integer. At a half-integer $$x = n + \frac{1}{2}$$, the function $$\left[x + \frac{1}{2}\right]$$ jumps by 1 (causing a discontinuity of $$+9$$) while $$[x]$$ is continuous. Since the jump is $$9 \neq 0$$, $$g$$ is discontinuous at every half-integer. A function that is discontinuous at a point cannot be differentiable there.

In the interval $$(-20, 20)$$, the integers are $$-19, -18, \ldots, 18, 19$$, totalling 39 points. The half-integers are $$-19.5, -18.5, \ldots, 18.5, 19.5$$, totalling 40 points. The point $$x = -\frac{3}{2}$$ where the absolute value term is non-differentiable is already counted among the half-integers.

Therefore the total number of points where $$f$$ is not differentiable is $$39 + 40 = 79$$.

Hence, the correct answer is $$\boxed{79}$$.

We have $$f(x) = \begin{cases} \{4x^2 - 8x + 5\}, & \text{if } 8x^2 - 6x + 1 \ge 0 \\ [4x^2 - 8x + 5], & \text{if } 8x^2 - 6x + 1 < 0 \end{cases}$$ where $$\{\alpha\}$$ is the fractional part and $$[\alpha]$$ is the greatest integer function.

Observe that $$g(x) = 4x^2 - 8x + 5 = 4(x-1)^2 + 1$$.

Since $$g$$ attains its minimum at $$x = 1$$, this minimum value is $$g(1) = 1$$.

Moreover, $$g$$ is symmetric about $$x = 1$$.

To determine the intervals where each branch of $$f$$ applies, we solve $$8x^2 - 6x + 1 = 0$$.

$$8x^2 - 6x + 1 = (2x - 1)(4x - 1) = 0 \implies x = \dfrac{1}{4} \text{ or } x = \dfrac{1}{2}$$

It follows that $$8x^2 - 6x + 1 < 0$$ on $$\left(\dfrac{1}{4},\, \dfrac{1}{2}\right)$$ and is non-negative elsewhere.

Hence $$f(x) = \{g(x)\}$$ outside $$\left(\dfrac{1}{4},\, \dfrac{1}{2}\right)$$ and $$f(x) = [g(x)]$$ on $$\left(\dfrac{1}{4},\, \dfrac{1}{2}\right)$$.

In particular, evaluating $$g$$ at the endpoints of $$\left(\dfrac{1}{4},\, \dfrac{1}{2}\right)$$ yields:

$$g\!\left(\dfrac{1}{4}\right) = 4\!\left(\dfrac{3}{4}\right)^2 + 1 = 4 \cdot \dfrac{9}{16} + 1 = \dfrac{13}{4} = 3.25$$

$$g\!\left(\dfrac{1}{2}\right) = 4\!\left(\dfrac{1}{2}\right)^2 + 1 = 4 \cdot \dfrac{1}{4} + 1 = 2$$

Thus, on $$\left(\dfrac{1}{4},\, \dfrac{1}{2}\right)$$, $$g$$ decreases from $$3.25$$ to $$2$$.

Within this interval, the value of $$[g(x)]$$ depends on whether $$g(x)$$ lies in $$[3,3.25)$$ or $$[2,3)$$.

In particular, $$[g(x)]$$ equals $$3$$ when $$g(x)\in[3,3.25)$$ and equals $$2$$ when $$g(x)\in[2,3)$$.

Solving $$g(x)=3\implies (x-1)^2=\dfrac{1}{2}\implies x=1-\dfrac{1}{\sqrt{2}}\approx 0.293$$.

Since this value lies in $$\left(\dfrac{1}{4},\, \dfrac{1}{2}\right)$$, the floor function jumps from $$3$$ to $$2$$ at that point.

Next, examining the endpoints of $$\left(\dfrac{1}{4},\, \dfrac{1}{2}\right)$$, we find the following left and right limits of $$f(x)$$.

At $$x = \dfrac{1}{4}$$: from the left, $$f = \{g(1/4)\} = \{3.25\} = 0.25$$; from the right, $$f = [g(1/4^+)] = 3$$. There is a jump discontinuity.

At $$x = \dfrac{1}{2}$$: from the left, $$f = [g(1/2^-)] = 2$$; from the right, $$f = \{g(1/2)\} = \{2\} = 0$$. There is a jump discontinuity.

Therefore, the non-differentiable points occur at

(1) $$x = \dfrac{1}{4}$$: discontinuity between the two branches.

(2) $$x = 1 - \dfrac{1}{\sqrt{2}}$$: floor function jumps from $$3$$ to $$2$$.

(3) $$x = \dfrac{1}{2}$$: discontinuity between the two branches.

Thus, the answer is $$3$$.

We need to check continuity at $$x = 0$$ for $$f(x) = \frac{\cos^{-1}(1 - \{x\}^2)\sin^{-1}(1 - \{x\})}{\{x\} - \{x\}^3}$$ where $$\{x\} = x - [x]$$.

For the right-hand limit ($$x \to 0^+$$): $$\{x\} = x$$, so $$f(x) = \frac{\cos^{-1}(1 - x^2)\sin^{-1}(1 - x)}{x - x^3} = \frac{\cos^{-1}(1 - x^2)\sin^{-1}(1 - x)}{x(1 - x^2)}$$.

As $$x \to 0^+$$: Using the approximation $$\cos^{-1}(1 - t) \approx \sqrt{2t}$$ for small $$t$$, we get $$\cos^{-1}(1 - x^2) \approx x\sqrt{2}$$. Also, $$\sin^{-1}(1 - x) \to \sin^{-1}(1) = \frac{\pi}{2}$$ and $$1 - x^2 \to 1$$.

So the right-hand limit $$= \frac{x\sqrt{2} \cdot \frac{\pi}{2}}{x \cdot 1} = \frac{\pi}{\sqrt{2}}$$.

For the left-hand limit ($$x \to 0^-$$): Let $$x = -\varepsilon$$ where $$\varepsilon \to 0^+$$. Then $$[x] = -1$$, so $$\{x\} = x - (-1) = 1 - \varepsilon$$.

Now $$1 - \{x\}^2 = 1 - (1-\varepsilon)^2 = 2\varepsilon - \varepsilon^2 \to 0$$, so $$\cos^{-1}(1 - \{x\}^2) \to \cos^{-1}(0) = \frac{\pi}{2}$$.

Also $$1 - \{x\} = \varepsilon$$, so $$\sin^{-1}(1 - \{x\}) = \sin^{-1}(\varepsilon) \approx \varepsilon$$.

The denominator: $$\{x\} - \{x\}^3 = (1-\varepsilon)(1-(1-\varepsilon)^2) = (1-\varepsilon)\varepsilon(2-\varepsilon) \approx 2\varepsilon$$.

So the left-hand limit $$= \frac{\frac{\pi}{2} \cdot \varepsilon}{2\varepsilon} = \frac{\pi}{4}$$.

Since the right-hand limit $$\frac{\pi}{\sqrt{2}} \neq \frac{\pi}{4}$$ (the left-hand limit), the function cannot be made continuous at $$x = 0$$. Therefore, no such $$\alpha$$ exists.

We have $$f(x) = [x] \cos\left(\frac{2x - 1}{2}\pi\right)$$, where $$[x]$$ denotes the greatest integer function.

We know that $$[x]$$ is discontinuous at every integer. So we check the behaviour of $$f$$ at any integer $$n$$.

At $$x = n$$ (an integer): $$f(n) = [n] \cdot \cos\left(\frac{2n - 1}{2}\pi\right) = n \cdot \cos\left(n\pi - \frac{\pi}{2}\right)$$.

Now $$\cos\left(n\pi - \frac{\pi}{2}\right) = \cos(n\pi)\cos\left(\frac{\pi}{2}\right) + \sin(n\pi)\sin\left(\frac{\pi}{2}\right) = 0 + 0 = 0$$.

So $$f(n) = 0$$ for every integer $$n$$.

As $$x \to n$$, we have $$[x] \to n$$ or $$n - 1$$ (from the left), which is bounded, and $$\cos\left(\frac{2x - 1}{2}\pi\right) \to \cos\left(\frac{2n - 1}{2}\pi\right) = 0$$.

So $$\lim_{x \to n} f(x) = (\text{bounded}) \times 0 = 0 = f(n)$$.

Since the only possible points of discontinuity are at integers, and the function is continuous at every integer, $$f$$ is continuous for every real $$x$$.

Hence, the correct answer is Option D.

For $$f(x)$$ to be continuous on $$\mathbb{R}$$, it must be continuous at $$x = -1$$ and $$x = 1$$.

At $$x = 1$$: from the right, $$\displaystyle\lim_{x \to 1^+} \sin(\pi x) = \sin\pi = 0$$. From the middle piece, $$f(1) = |a + 1 + b|$$. For continuity, $$|a + 1 + b| = 0$$, so $$a + b = -1$$.

At $$x = -1$$: from the left, $$\displaystyle\lim_{x \to -1^-} 2\sin\left(-\dfrac{\pi x}{2}\right) = 2\sin\left(\dfrac{\pi}{2}\right) = 2$$. From the middle piece, $$f(-1) = |a - 1 + b| = |a + b - 1| = |-1 - 1| = |-2| = 2$$. This is consistent, confirming continuity at $$x = -1$$.

Therefore $$a + b = -1$$.

For $$x<2,$$ we have

$$x^2-5x+6=(x-2)(x-3)$$

Since $$x<2,$$ both $$x-2<0$$ and $$x-3<0.$$ Hence,

$$(x-2)(x-3)>0$$

Therefore,

$$|x^2-5x+6|=x^2-5x+6$$

Also,

$$5x-x^2-6=-(x^2-5x+6)$$

Thus,

$$f(x)=\frac{\lambda(x^2-5x+6)}{-\mu(x^2-5x+6)}=-\frac{\lambda}{\mu}$$

Hence,

$$\lim_{x\to2^-}f(x)=-\frac{\lambda}{\mu}$$

Now evaluate the right-hand limit.

For $$2<x<3,$$ we have

$$[x]=2$$

Therefore,

$$x-[x]=x-2$$

Hence,

$$\lim_{x\to2^+}e^{\frac{\tan(x-2)}{x-[x]}}=\lim_{x\to2^+}e^{\frac{\tan(x-2)}{x-2}}$$

Using

$$\lim_{t\to0}\frac{\tan t}{t}=1,$$

we get

$$\lim_{x\to2^+}f(x)=e$$

Since $$f$$ is continuous at $$x=2,$$

$$-\frac{\lambda}{\mu}=e=\mu$$

Hence,

$$\mu=e$$ and $$-\frac{\lambda}{e}=e$$

$$\lambda=-e^2$$

Therefore,

$$\lambda+\mu=-e^2+e=e(1-e)$$

For continuity we need to check the two potential discontinuities at $$x = 0$$ and $$x = 1$$.

At $$x = 0$$: The left-hand limit is $$\lim_{x \to 0^-}(\sin x - e^x) = \sin 0 - e^0 = -1$$. For the right-hand limit, when $$0 < x < 1$$, we have $$-1 < -x < 0$$, so $$[-x] = -1$$. Thus the right-hand limit is $$\lim_{x \to 0^+}(a + [-x]) = a - 1$$. Setting equal: $$a - 1 = -1$$, giving $$a = 0$$.

At $$x = 1$$: For the left-hand limit, as $$x \to 1^-$$ with $$0 < x < 1$$, we have $$-x \to -1^+$$, so $$[-x] = -1$$. Thus the left-hand limit is $$0 + (-1) = -1$$. The right-hand value is $$2(1) - b = 2 - b$$. Setting equal: $$2 - b = -1$$, giving $$b = 3$$.

Therefore $$a + b = 0 + 3 = 3$$.

We are given the function $$f : [0,\infty) \to [0,\infty)$$ defined by the rule

$$f(x)=\int_{0}^{x}[y]\,dy,$$

where $$[y]$$ denotes the greatest integer less than or equal to $$y$$ (the “floor-function”). Our task is to test the four statements about the continuity and differentiability of $$f$$.

First we must understand the exact algebraic form of $$f(x)$$ on every sub-interval between two consecutive integers. Let us take an arbitrary non-negative integer $$n$$ and look at all $$x$$ that satisfy

$$n\le x<n+1.$$

For any such $$x$$ we always have $$[y]=n$$ whenever the variable of integration $$y$$ itself satisfies $$n\le y<n+1$$. Hence, over the interval $$[n,n+1)$$, the integrand is the constant $$n$$. To integrate from 0 to $$x$$ we split the whole range $$[0,x]$$ into unit pieces:

$$ \int_{0}^{x}[y]\,dy =\int_{0}^{1}[y]\,dy +\int_{1}^{2}[y]\,dy +\cdots +\int_{n-1}^{n}[y]\,dy +\int_{n}^{x}[y]\,dy. $$

On each earlier unit interval $$[k,k+1]$$ (where $$k=0,1,\dots ,n-1$$) the integrand equals the integer $$k$$. Relying on the fact that the length of every such interval is exactly 1, we evaluate them one by one:

$$ \int_{k}^{k+1}[y]\,dy=\int_{k}^{k+1}k\,dy =k\int_{k}^{k+1}dy =k(1)=k. $$

Hence the sum of the first $$n$$ integrals is

$$ \sum_{k=0}^{n-1}k =0+1+2+\dots +(n-1). $$

We recall the formula for the sum of the first $$m$$ natural numbers:

$$ 0+1+2+\dots +m=\frac{m(m+1)}{2}. $$

Using $$m=n-1$$ we get

$$ \sum_{k=0}^{n-1}k=\frac{(n-1)n}{2}. $$

The last part of the integral is over $$[n,x]$$ where the integrand is the constant $$n$$. Its value is

$$ \int_{n}^{x}n\,dy =n\int_{n}^{x}dy =n(x-n). $$

Combining everything, for every $$x$$ with $$n\le x<n+1$$ we have

$$ f(x)=\frac{(n-1)n}{2}+n(x-n). $$

That is an explicit linear expression in $$x$$ inside each open interval $$(n,n+1).$$ Now we test continuity at the integer point $$x=n.$$ We must compare the left-hand limit, the value actually taken, and the right-hand limit.

Left-hand limit as $$x\to n^-$$ (use the formula with $$n-1$$ because $$x$$ lies in $$(n-1,n)$$):

$$ \lim_{x\to n^-}f(x) =\frac{(n-2)(n-1)}{2}+(n-1)\bigl(n-(n-1)\bigr) =\frac{(n-2)(n-1)}{2}+(n-1)(1). $$

Simplifying term by term,

$$ (n-1)(1)=n-1, $$

so

$$ \frac{(n-2)(n-1)}{2}+n-1 =\frac{(n-1)\bigl(n-2+2\bigr)}{2} =\frac{(n-1)n}{2}. $$

Now the actual value when $$x=n$$ is obtained by direct substitution in the defining integral:

$$ f(n)=\int_{0}^{n}[y]\,dy. $$

Everything up to $$y=n$$ has been covered earlier, hence

$$ f(n)=\frac{(n-1)n}{2}, $$

the same number that just appeared.

Right-hand limit as $$x\to n^+$$ (use the formula with $$n$$ because now $$x$$ lies in $$(n,n+1)$$):

$$ \lim_{x\to n^+}f(x) =\frac{(n-1)n}{2}+n\bigl(n-n\bigr) =\frac{(n-1)n}{2}+n\cdot0 =\frac{(n-1)n}{2}. $$

Therefore the left-hand limit, the value at $$x=n$$, and the right-hand limit are identical. Hence $$f$$ is continuous at every integer, and of course it is linear (hence continuous) on every open interval between integers. All together, $$f$$ is continuous on the whole half-line $$[0,\infty).$$

Now we turn to differentiability. Whenever $$x$$ lies strictly between two integers, say $$n<x<n+1,$$ the integrand $$[y]$$ is continuous at $$y=x$$, so the Fundamental Theorem of Calculus (stated as “If $$F(x)=\int_{a}^{x}g(t)dt$$ and $$g$$ is continuous at $$x$$ then $$F'(x)=g(x)$$”) applies. Hence

$$ f'(x)=[x]=n \quad\text{for }n<x<n+1. $$

Thus $$f'(x)$$ exists and equals a constant integer on every open interval between integers.

Finally, examine differentiability at the integer point $$x=n$$ itself. The derivative, if it exists, must match the two one-sided limits of the difference quotient. We compute:

Left-hand derivative

$$ \lim_{h\to0^-}\frac{f(n+h)-f(n)}{h} =\lim_{h\to0^-}\frac{(n-1)(n-2)/2+(n-1)(h+1)-\frac{(n-1)n}{2}}{h} =\lim_{h\to0^-}\frac{(n-1)h}{h}=n-1. $$

Right-hand derivative

$$ \lim_{h\to0^+}\frac{f(n+h)-f(n)}{h} =\lim_{h\to0^+}\frac{\frac{(n-1)n}{2}+n\,h-\frac{(n-1)n}{2}}{h} =\lim_{h\to0^+}\frac{n\,h}{h}=n. $$

Because $$n-1\ne n,$$ the two one-sided derivatives are unequal, so $$f'(n)$$ does not exist. Therefore $$f$$ is not differentiable at any integer, but it is differentiable everywhere else.

Gathering all conclusions:

• $$f$$ is continuous at every point of $$[0,\infty).$$
• $$f$$ fails to be differentiable precisely at the integers and is differentiable everywhere else.

This matches exactly the wording of Option A.

Hence, the correct answer is Option A.

For continuity at $$x=0,$$ we require

$$\alpha=\lim_{x\to0}\frac{x^3}{(1-\cos2x)^2}\log_e\left(\frac{1+2xe^{-2x}}{(1-xe^{-x})^2}\right)$$

Using $$1-\cos2x=2\sin^2x,$$

we get $$(1-\cos2x)^2=4\sin^4x$$

Hence,

$$\alpha=\lim_{x\to0}\frac{x^3}{4\sin^4x}\log_e\left(\frac{1+2xe^{-2x}}{(1-xe^{-x})^2}\right)$$

Therefore,

$$\alpha=\frac14\lim_{x\to0}\left(\frac{x}{\sin x}\right)^4\frac1x\log_e\left(\frac{1+2xe^{-2x}}{(1-xe^{-x})^2}\right)$$

Since

$$\lim_{x\to0}\frac{\sin x}{x}=1,$$

we obtain

$$\alpha=\frac14\lim_{x\to0}\frac1x\log_e\left(\frac{1+2xe^{-2x}}{(1-xe^{-x})^2}\right)$$

Using logarithmic properties,

$$\log_e\left(\frac{1+2xe^{-2x}}{(1-xe^{-x})^2}\right)=\log_e(1+2xe^{-2x})-2\log_e(1-xe^{-x})$$

Now,

$$e^{-2x}=1-2x+O(x^2),\qquad e^{-x}=1-x+O(x^2)$$

Hence,

$$2xe^{-2x}=2x+O(x^2),\qquad xe^{-x}=x+O(x^2)$$

Using

$$\log(1+t)=t+O(t^2),$$

we get

$$\log_e(1+2xe^{-2x})=2x+O(x^2)$$

and

$$-2\log_e(1-xe^{-x})=2x+O(x^2)$$

Therefore,

$$\log_e\left(\frac{1+2xe^{-2x}}{(1-xe^{-x})^2}\right)=4x+O(x^2)$$

Thus,

$$\alpha=\frac14\lim_{x\to0}\frac{4x+O(x^2)}x$$

$$=\frac14\cdot4$$

$$=1$$

Given $$f(x) = x^3 - ax^2 + bx - 4$$ on $$[1, 2]$$ with Rolle's theorem applicable, we need $$f(1) = f(2)$$ and $$f'\left(\frac{4}{3}\right) = 0$$.

Computing $$f(1) = 1 - a + b - 4 = -3 - a + b$$ and $$f(2) = 8 - 4a + 2b - 4 = 4 - 4a + 2b$$.

Setting $$f(1) = f(2)$$: $$-3 - a + b = 4 - 4a + 2b$$, which simplifies to $$3a - b = 7$$ ... (i).

Now $$f'(x) = 3x^2 - 2ax + b$$. Setting $$f'\left(\frac{4}{3}\right) = 0$$: $$3 \cdot \frac{16}{9} - 2a \cdot \frac{4}{3} + b = 0$$, which gives $$\frac{16}{3} - \frac{8a}{3} + b = 0$$. Multiplying by 3: $$16 - 8a + 3b = 0$$ ... (ii).

From (i): $$b = 3a - 7$$. Substituting into (ii): $$16 - 8a + 3(3a - 7) = 0$$, which gives $$16 - 8a + 9a - 21 = 0$$, so $$a - 5 = 0$$, hence $$a = 5$$.

Then $$b = 3(5) - 7 = 8$$.

Therefore, the ordered pair $$(a, b) = (5, 8)$$.

We want the function to be continuous at $$x = 0$$, so the left-hand limit, the value at the point, and the right-hand limit must all be equal. In symbols:

$$\lim_{x \to 0^-} f(x) \;=\; f(0) \;=\; \lim_{x \to 0^+} f(x).$$

First we examine $$x \to 0^-$$. For $$x < 0$$ we have

$$f(x) \;=\; (1 + |\sin x|)^{\dfrac{3a}{|\sin x|}}.$$

Because $$x < 0$$, $$\sin x < 0$$ and therefore $$|\sin x| = -\sin x$$. Put $$t = |\sin x|$$; then as $$x \to 0^-$$ we get $$t \to 0^+$$. We now recall the standard limit formula

$$\lim_{t \to 0} (1 + t)^{\frac{k}{t}} \;=\; e^{\,k}.$$

Comparing, we see $$k = 3a$$, so

$$\lim_{x \to 0^-} f(x) \;=\; \lim_{t \to 0^+} (1 + t)^{\frac{3a}{t}} \;=\; e^{\,3a}.$$

Next we examine $$x \to 0^+$$. For $$0 < x < \dfrac{\pi}{4}$$ we have

$$f(x) \;=\; e^{\frac{\cot 4x}{\cot 2x}}.$$

We need $$\displaystyle \lim_{x \to 0^+} \frac{\cot 4x}{\cot 2x}$$. Using the small-angle expansion $$\cot \theta \approx \dfrac{1}{\theta}$$ (the dominant term as $$\theta \to 0$$), we get

$$\cot 4x \;\approx\; \frac{1}{4x}, \qquad \cot 2x \;\approx\; \frac{1}{2x}.$$

Hence

$$\frac{\cot 4x}{\cot 2x} \;\approx\; \frac{\dfrac{1}{4x}}{\dfrac{1}{2x}} \;=\; \frac{1}{4x}\cdot 2x \;=\; \frac12.$$

Therefore

$$\lim_{x \to 0^+} f(x) \;=\; e^{\frac12} \;=\; e^{\,1/2}.$$

Now let $$f(0) = b$$. Continuity demands

$$e^{\,3a} = b = e^{\,1/2}.$$

Equating the exponents in the first equality gives

$$3a = \frac12 \;\Longrightarrow\; a = \frac16.$$

The second equality already gives

$$b = e^{\,1/2}.$$

We now compute the required expression:

$$6a + b^2 \;=\; 6\bigl(\tfrac16\bigr) + \bigl(e^{\,1/2}\bigr)^2 \;=\; 1 + e.$$

Hence, the correct answer is Option 3.

We begin with the three functions that have been defined:

$$f(x)=x-[x],\qquad g(x)=1-x+[x],\qquad h(x)=\min\{f(x),g(x)\},\qquad x\in[-2,2].$$

Here $$[t]$$ denotes the greatest integer less than or equal to $$t$$ (the floor function). For every real number $$x$$ we can write $$x=[x]+\{x\},$$ where $$\{x\}=x-[x]$$ is the fractional part of $$x$$ and satisfies $$0\le\{x\}\lt 1.$$ Hence, for every $$x,$$

$$f(x)=\{x\}\qquad\text{and}\qquad g(x)=1-\{x\}.$$

Because $$0\le\{x\}\lt 1,$$ it follows that

$$0\le f(x)\lt 1,\qquad 0\lt g(x)\le1,\qquad f(x)+g(x)=1.$$

Let us examine the behaviour of $$f(x)$$ and $$g(x)$$ on a typical integral interval. Fix an integer $$n$$; then for every $$x$$ in the half-open interval $$n\le x\lt n+1$$ we have $$[x]=n$$ and hence

$$f(x)=x-n,\qquad g(x)=1-(x-n)=1-f(x).$$

Inside this interval $$f(x)$$ increases linearly from $$0$$ up to $$1^{-}$$ while $$g(x)$$ decreases linearly from $$1$$ down to $$0^{+}.$$ Now we find where the two graphs meet. We solve

$$f(x)=g(x)\;\;\Longrightarrow\;\;x-n=1-(x-n)\;\;\Longrightarrow\;\;2(x-n)=1\;\;\Longrightarrow\;\;x=n+\tfrac12.$$

So the only point of intersection in the interval $$[n,n+1)$$ is at $$x=n+\dfrac12,$$ where both $$f$$ and $$g$$ take the value $$\dfrac12.$$ Therefore, in that interval

$$\begin{cases} f(x)\lt g(x)&\text{for}\;n\le x\lt n+\dfrac12,\\[4pt] f(x)=g(x)&\text{for}\;x=n+\dfrac12,\\[4pt] f(x)\gt g(x)&\text{for}\;n+\dfrac12\lt x\lt n+1. \end{cases}$$

Because $$h(x)=\min\{f(x),g(x)\},$$ we deduce the explicit description

$$ h(x)= \begin{cases} f(x)=x-n,& & n\le x\le n+\dfrac12,\\[6pt] g(x)=1-x+n,& & n+\dfrac12\le x\lt n+1. \end{cases} $$

Thus, on each integral interval $$[n,n+1)$$ the graph of $$h$$ is a “V”-shaped line: it rises with slope $$+1$$ from $$0$$ up to $$\dfrac12$$ and then falls with slope $$-1$$ back to $$0.$$ Next we study continuity.

Continuity at interior points of an interval $$ (n,n+1) $$. Inside $$ (n,n+1) $$ the formula for $$ h $$ is linear, so $$ h $$ is continuous there.

Continuity at the midpoint $$ n+\tfrac12 $$. The left-hand limit equals the common value $$\dfrac12,$$ the right-hand limit also equals $$\dfrac12,$$ and $$h(n+\tfrac12)=\dfrac12.$$ Hence the function is continuous at the midpoint.

Continuity at an integer $$ n $$.

Approaching $$ n $$ from the left we are in the interval $$ (n-\tfrac12,n) $$ where $$h(x)=g(x)=1-(x-n)=n+1-x.$$ Taking the limit as $$ x\to n^- $$ gives $$\displaystyle\lim_{x\to n^-}h(x)=1-(n-n)=0.$$

Approaching $$ n $$ from the right we are in the interval $$ (n,n+\tfrac12) $$ where $$h(x)=f(x)=x-n.$$ Taking the limit as $$ x\to n^+ $$ gives $$\displaystyle\lim_{x\to n^+}h(x)=n-n=0.$$

The value of the function at the integer itself is $$h(n)=\min\bigl\{f(n)=0,\;g(n)=1\bigr\}=0.$$ Since the left-hand limit, the right-hand limit and the value are all equal, $$ h $$ is continuous at every integer.

Because the above discussion covers every point in the domain, we conclude that $$h(x)$$ is continuous on the whole closed interval $$[-2,2].$$

Now we analyse differentiability. We first compute the derivative in the open sub-intervals where the formula is linear.

For $$n\lt x\lt n+\dfrac12,\qquad h(x)=x-n\;\Longrightarrow\;h'(x)=1.$$ For $$n+\dfrac12\lt x\lt n+1,\qquad h(x)=1-x+n\;\Longrightarrow\;h'(x)=-1.$$

Thus, inside each linear segment the derivative exists and equals $$\pm1.$$ Possible points of non-differentiability are therefore the junction points, namely

• all midpoints $$x=n+\dfrac12,$$ • all integers $$x=n.$$ Let us check each of these.

At a midpoint $$ n+\tfrac12 $$. Left-hand derivative $$h'_- = 1,$$ right-hand derivative $$h'_+ = -1.$$ Since the one-sided derivatives are unequal, $$ h $$ is not differentiable here.

At an integer $$ n $$. Left-hand derivative (coming from the segment with slope $$-1$$) equals $$-1,$$ right-hand derivative (coming from the segment with slope $$+1$$) equals $$+1.$$ Again the derivatives are unequal, so $$ h $$ is not differentiable here either.

Within the open interval $$(-2,2)$$ the integers that occur are $$-1,\,0,\,1$$ (three points). The midpoints that occur are

$$-1.5,\;-0.5,\;0.5,\;1.5$$

(four points). Hence, inside $$(-2,2)$$ the total number of non-differentiable points is

$$3+4=7,$$

which is certainly “more than four.”

Combining the two conclusions we have:

• $$ h $$ is continuous on $$[-2,2].$$ • $$ h $$ fails to be differentiable at seven points of $$(-2,2).$$

This description matches exactly Option A, which states “continuous in $$[-2,2]$$ but not differentiable at more than four points in $$(-2,2).$$”

Hence, the correct answer is Option A.

We have $$f(x) = \begin{cases} x+2, & x < 0 \\ x^2, & x \geq 0 \end{cases}$$ and $$g(x) = \begin{cases} x^3, & x < 1 \\ 3x-2, & x \geq 1 \end{cases}$$. We need to find where $$(f \circ g)(x) = f(g(x))$$ is not differentiable.

For $$x < 0$$: $$g(x) = x^3 < 0$$, so $$f(g(x)) = x^3 + 2$$. For $$0 \leq x < 1$$: $$g(x) = x^3 \geq 0$$, so $$f(g(x)) = (x^3)^2 = x^6$$. For $$x \geq 1$$: $$g(x) = 3x - 2 \geq 1 > 0$$, so $$f(g(x)) = (3x-2)^2$$.

At $$x = 0$$: From the left, $$\lim_{x \to 0^-}(x^3 + 2) = 2$$. From the right, $$\lim_{x \to 0^+} x^6 = 0$$. Also $$f(g(0)) = f(0) = 0$$. Since the left-hand limit does not equal the function value, $$f \circ g$$ is not continuous (hence not differentiable) at $$x = 0$$.

At $$x = 1$$: From the left, $$\lim_{x \to 1^-} x^6 = 1$$. From the right, $$(3(1)-2)^2 = 1$$. So $$f \circ g$$ is continuous at $$x = 1$$. The left derivative is $$6x^5|_{x=1} = 6$$ and the right derivative is $$2(3x-2)(3)|_{x=1} = 6$$. Since both derivatives are equal, $$f \circ g$$ is differentiable at $$x = 1$$.

Therefore, there is exactly 1 point in $$\mathbb{R}$$ where $$(f \circ g)(x)$$ is not differentiable.

We have a composite function

$$f(x)=\;|x^{2}-2x-3|\; \cdot e^{\,9x^{2}-12x+4}$$

To locate the points where $$f(x)$$ is not differentiable, we first note that the exponential part $$e^{\,9x^{2}-12x+4}$$ is an elementary exponential function. An exponential function of the form $$e^{g(x)}$$ is differentiable for every real number because its derivative is

$$\dfrac{d}{dx}\bigl(e^{g(x)}\bigr)=g'(x)\,e^{g(x)},$$

and both $$g(x)$$ and $$g'(x)$$ are polynomials here. Therefore, any loss of differentiability can occur only because of the modulus (absolute-value) factor $$|x^{2}-2x-3|$$.

A function of the type $$|u(x)|$$ is differentiable everywhere except possibly at those values of $$x$$ where its inside expression $$u(x)$$ equals zero. Hence, we first solve

$$x^{2}-2x-3 = 0.$$

We factor the quadratic:

$$x^{2}-2x-3=(x-3)(x+1).$$

Setting each factor to zero gives

$$x-3=0 \;\Longrightarrow\; x = 3,$$

$$x+1=0 \;\Longrightarrow\; x = -1.$$

Thus the inside of the modulus vanishes precisely at

$$x=-1 \quad\text{and}\quad x=3.$$

Next, we verify that differentiability indeed fails at these two points. Whenever $$u(x)=0,$$ the expression $$|u(x)|$$ changes from $$u(x)$$ on one side to $$-u(x)$$ on the other. This causes the left-hand derivative (LHD) and the right-hand derivative (RHD) of the overall function to differ, because the sign of $$u(x)$$ flips. Consequently the derivative does not exist at those points.

At every other point, $$x^{2}-2x-3\neq0,$$ so the modulus simply contributes a factor of either $$+1$$ or $$-1,$$ and both the modulus and the exponential part are smooth there. Hence the product remains differentiable.

Therefore the function loses differentiability only at

$$x=-1 \quad\text{and}\quad x=3,$$

giving exactly two distinct points of non-differentiability.

Hence, the correct answer is Option B.

We have been given a piece-wise definition

and are told that the function is continuous at the point $$x=0$$. For continuity we must have

We shall therefore compute the left-hand limit (LHL) and the right-hand limit (RHL) separately and then equate them to $$k$$.

Left-hand limit

The expression to be handled for $$x<0$$ is

For small $$x,$$ use the series expansion

Put

Then

Therefore

Dividing by $$x$$ and letting $$x\to 0^-$$ gives

Right-hand limit

For $$x>0$$ we have

Recall the double-angle identity

Hence the numerator is $$\cos 2x-1$$. Using the Maclaurin series

we obtain

For the denominator employ the binomial expansion of the square root:

so

Now form the quotient:

Letting $$x\to 0^+$$ we get

Equating the limits to $$k$$

Required expression

That value corresponds to Option D.

We are given a function $$f : [0,\infty) \to [0,3]$$ defined by

$$ f(x)= \begin{cases} \displaystyle\max\{\sin t \;:\; 0\le t\le\pi\}, & 0\le x\le\pi,\\[4pt] 2+\cos x, & x>\pi. \end{cases} $$

On the interval $$[0,\pi]$$ the expression $$\max\{\sin t : 0\le t\le\pi\}$$ is a single real number, because for all real numbers $$t$$ in that closed interval the function $$\sin t$$ attains its largest value at $$t=\dfrac{\pi}{2}$$. We know the familiar fact

$$ \sin\Bigl(\dfrac{\pi}{2}\Bigr)=1\quad\text{and}\quad 0\le\sin t\le 1\text{ for }0\le t\le\pi. $$

Hence the maximum is actually the constant $$1$$. Therefore, for every $$x$$ with $$0\le x\le\pi$$ we have

$$ f(x)=1. $$

So we can rewrite the definition in a simpler two-piece form:

$$ f(x)= \begin{cases} 1, & 0\le x\le\pi,\\[6pt] 2+\cos x, & x>\pi. \end{cases} $$

Now we examine continuity and differentiability.

1. Continuity inside each open sub-interval.

• For $$0<x<\pi$$ the function is the constant $$1$$, which is continuous.

• For $$x>\pi$$ the expression $$2+\cos x$$ is a sum of continuous functions, hence continuous.

Therefore inside the separate pieces $$f$$ is continuous.

2. Continuity at the junction $$x=\pi$$.

We compute the left-hand value, the right-hand value and the limit.

Left value and left limit:

$$ \lim_{x\to\pi^-}f(x)=1,\qquad f(\pi)=1. $$

Right limit:

$$ \lim_{x\to\pi^+}f(x)=\lim_{x\to\pi^+}(2+\cos x)=2+\cos\pi=2-1=1. $$

Because left limit, right limit and the actual value are all equal to $$1$$, the function is continuous at $$x=\pi$$.

3. Differentiability inside each open sub-interval.

• For $$0<x<\pi$$ the function is constant, so

$$ f'(x)=0\quad\text{for }0<x<\pi. $$

• For $$x>\pi$$ we differentiate $$2+\cos x$$. Using the standard derivative $$\dfrac{d}{dx}(\cos x)=-\sin x$$, we get

$$ f'(x)=-\sin x\quad\text{for }x>\pi. $$

Thus $$f$$ is differentiable at every point inside the two pieces.

4. Differentiability at the junction $$x=\pi$$.

To check differentiability at a boundary point we must verify that the left-hand derivative and the right-hand derivative exist and are equal.

Left-hand derivative (using the constant piece):

$$ f'_-(\pi)=\lim_{h\to0^-}\frac{f(\pi+h)-f(\pi)}{h} =\lim_{h\to0^-}\frac{1-1}{h}=0. $$

Right-hand derivative (using the second piece):

Starting with the formula $$f(x)=2+\cos x$$ for $$x>\pi$$ and differentiating, we have $$f'(x)=-\sin x$$. Therefore

$$ f'_+(\pi)=\lim_{h\to0^+}\frac{f(\pi+h)-f(\pi)}{h} =\left[-\sin x\right]_{x=\pi}= -\sin\pi = 0. $$

The two one-sided derivatives are equal and finite, so $$f$$ is differentiable at $$x=\pi$$ as well.

5. Differentiability on $$(0,\infty)$$.

We have now shown that for every point $$x$$ with $$0<x<\pi$$, for every point $$x$$ with $$x>\pi$$, and also at the critical point $$x=\pi$$ itself, the derivative exists. Therefore $$f$$ is differentiable everywhere in the open interval $$(0,\infty)$$.

6. Final choice.

Among the options, the only statement that matches our conclusion is:

Option B: “$$f$$ is differentiable everywhere in $$(0,\infty)$$.”

Hence, the correct answer is Option B.

We have a function $$f$$ that is continuous on $$[0,2]$$ and twice differentiable on $$(0,2)$$ with the data $$f(0)=0,\;f(1)=1,\;f(2)=2$$. In order to bring the three equal ​end-values required by Rolle’s Theorem into the problem, let us introduce a new auxiliary function

$$g(x)=f(x)-x.$$

This simple subtraction is motivated by the desire to “cancel’’ the given values of $$f$$ at the three integer points. Indeed, substituting $$x=0,1,2$$ we obtain

$$\begin{aligned} g(0)&=f(0)-0 =0,\\ g(1)&=f(1)-1 =0,\\ g(2)&=f(2)-2 =0. \end{aligned}$$

Thus $$g$$ is continuous on $$[0,2]$$, differentiable (in fact twice differentiable) on $$(0,2)$$, and it satisfies $$g(0)=g(1)=g(2)=0$$.

Now recall the statement of Rolle’s Theorem: “If a function is continuous on $$[a,b]$$, differentiable on $$(a,b)$$ and $$h(a)=h(b)$$, then there exists some $$c\in(a,b)$$ such that $$h'(c)=0.$$”

We apply Rolle’s Theorem first to the interval $$[0,1]$$ for the function $$g$$. Because $$g(0)=g(1)=0$$, there is a point $$c_{1}\in(0,1)$$ with

$$g'(c_{1})=0.$$

We repeat the same reasoning on the interval $$[1,2]$$. Since $$g(1)=g(2)=0$$, there is another point $$c_{2}\in(1,2)$$ satisfying

$$g'(c_{2})=0.$$

At this stage we know that $$g'$$ vanishes at two distinct points $$c_{1}$$ and $$c_{2}$$ lying strictly inside $$(0,2)$$. Because $$g'$$ is continuous on $$[c_{1},c_{2}]$$ and differentiable on $$(c_{1},c_{2})$$ (again a consequence of the differentiability properties of $$f$$), we can apply Rolle’s Theorem once more—but now to the derivative $$g'$$ itself—on the interval $$[c_{1},c_{2}]$$. Since $$g'(c_{1})=g'(c_{2})=0$$, there exists some point $$c\in(c_{1},c_{2})\subset(0,2)$$ such that

$$g''(c)=0.$$

But $$g(x)=f(x)-x$$, so differentiating twice gives $$g''(x)=f''(x)-0=f''(x).$$ Therefore

$$f''(c)=0\quad\text{for some }c\in(0,2).$$

This conclusion matches exactly Option C, which states “$$f''(x)=0$$ for some $$x\in(0,2).$$”

Observe furthermore that

• Option A (“$$f''(x)>0$$ for all $$x$$”) is impossible because we have just found a point where $$f''$$ equals zero.
• Option B (“$$f'(x)=0$$ for some $$x$$”) is not guaranteed; the example $$f(x)=x$$ satisfies all given conditions yet has $$f'(x)=1$$ everywhere.
• Option D (“$$f'(x)=0$$ for all $$x$$”) is certainly false for the same linear example.

Hence, the correct answer is Option C.

Given,

$$f(x)=\begin{cases}\dfrac{\sin(a+1)x+\sin2x}{2x},&x<0\\[4pt]b,&x=0\\[4pt]\dfrac{\sqrt{x+bx^3}-\sqrt{x}}{bx^{5/2}},&x>0\end{cases}$$

For continuity at

$$x=0,$$

we require

$$\text{LHL}=\text{RHL}=f(0)=b$$

First find the left-hand limit.

$$\text{LHL}=\lim_{x\to0^-}\frac{\sin(a+1)x+\sin2x}{2x}$$

$$=\frac12\left[\lim_{x\to0}\frac{\sin(a+1)x}{x}+\lim_{x\to0}\frac{\sin2x}{x}\right]$$

Using

$$\lim_{x\to0}\frac{\sin kx}{x}=k,$$

we get

$$\text{LHL}=\frac12\left((a+1)+2\right)$$

$$=\frac{a+3}{2}$$

Now find the right-hand limit.

$$\text{RHL}=\lim_{x\to0^+}\frac{\sqrt{x+bx^3}-\sqrt{x}}{bx^{5/2}}$$

Factor out

$$\sqrt{x}:$$

$$=\lim_{x\to0^+}\frac{\sqrt{x}\left(\sqrt{1+bx^2}-1\right)}{bx^{5/2}}$$

$$=\lim_{x\to0^+}\frac{\sqrt{1+bx^2}-1}{bx^2}$$

Rationalizing,

$$=\lim_{x\to0^+}\frac{(1+bx^2)-1}{bx^2\left(\sqrt{1+bx^2}+1\right)}$$

$$=\lim_{x\to0^+}\frac{1}{\sqrt{1+bx^2}+1}$$

$$=\frac12$$

Therefore,

$$b=\frac12$$

Now continuity gives

$$\frac{a+3}{2}=b=\frac12$$

Hence,

$$a+3=1$$

$$a=-2$$

Therefore,

$$a+b=-2+\frac12$$

$$=-\frac32$$

Hence, the required value is

$$\boxed{-\frac32}$$

We begin by writing the definition of the function clearly:

$$ f(x)= \begin{cases} \displaystyle\int_{0}^{x}\bigl(5+\lvert 1-t\rvert\bigr)\,dt, & x>2\\[6pt] 5x+1, & x\le 2 \end{cases} $$

The questions to check are continuity and differentiability at the points where the formula changes or where the integrand changes its algebraic form. The possible “trouble spots’’ are therefore $$x=2$$ (where the definition changes) and $$x=1$$ (where $$\lvert 1-t\rvert$$ changes its expression).

Step 1 : Continuity at $$x=2$$

We must compare the left-hand limit, the right-hand limit and the actual value.

Left value (or left limit) comes from the polynomial part because for $$x\le 2$$ we have $$f(x)=5x+1$$. Substituting $$x=2$$, we get

$$f(2^{-})=5\cdot 2+1=10+1=11.$$

Right value is obtained from the integral formula with the upper limit $$x=2$$:

$$ f(2^{+})=\int_{0}^{2}\bigl(5+\lvert 1-t\rvert\bigr)\,dt. $$

To compute the integral, we split the interval at the point where the absolute-value expression changes sign, namely $$t=1$$.

For $$0\le t\le 1$$, we have $$\lvert 1-t\rvert=1-t$$, so

$$5+\lvert 1-t\rvert = 5+(1-t)=6-t.$$

For $$1\le t\le 2$$, we have $$\lvert 1-t\rvert=t-1$$, so

$$5+\lvert 1-t\rvert = 5+(t-1)=4+t.$$

Hence,

$$ \begin{aligned} f(2^{+}) &= \int_{0}^{1}(6-t)\,dt \;+\;\int_{1}^{2}(4+t)\,dt\\[6pt] &=\Bigl[6t-\tfrac{t^{2}}{2}\Bigr]_{0}^{1}\;+\;\Bigl[4t+\tfrac{t^{2}}{2}\Bigr]_{1}^{2}. \end{aligned} $$

Evaluating each bracket,

$$ \begin{aligned} \Bigl[6t-\tfrac{t^{2}}{2}\Bigr]_{0}^{1}&=\left(6\cdot1-\tfrac{1^{2}}{2}\right)-0=6-\tfrac12=\tfrac{11}{2},\\[6pt] \Bigl[4t+\tfrac{t^{2}}{2}\Bigr]_{1}^{2}&=\left(4\cdot2+\tfrac{2^{2}}{2}\right)-\left(4\cdot1+\tfrac{1^{2}}{2}\right)\\ &=(8+2)-(4+\tfrac12)=10-4.5=\tfrac{11}{2}. \end{aligned} $$

Adding the two halves,

$$f(2^{+})=\tfrac{11}{2}+\tfrac{11}{2}=11.$$

Because $$f(2^{-})=11$$ and $$f(2^{+})=11$$, we have

$$\lim_{x\to 2}f(x)=f(2)=11.$$

Therefore $$f(x)$$ is continuous at $$x=2$$.

Step 2 : Differentiability at $$x=2$$

For $$x\lt 2$$ we use the simple polynomial part, so

$$f'(x)=\dfrac{d}{dx}(5x+1)=5.$$

Hence the left derivative at 2 is

$$f'(2^{-})=5.$$

For $$x\gt 2$$ we invoke the Fundamental Theorem of Calculus, which states that if

$$F(x)=\int_{a}^{x}g(t)\,dt,$$

then $$F'(x)=g(x)$$ provided $$g$$ is continuous at $$x$$. Here $$g(t)=5+\lvert 1-t\rvert$$ is continuous for all real $$t$$, so

$$f'(x)=5+\lvert 1-x\rvert,\qquad x\gt 2.$$

Substituting $$x=2$$ from the right,

$$f'(2^{+})=5+\lvert 1-2\rvert=5+1=6.$$

The left derivative equals 5 while the right derivative equals 6, i.e.

$$f'(2^{-})\ne f'(2^{+}).$$

Because the two one-sided derivatives are unequal, $$f(x)$$ is not differentiable at $$x=2$$.

Step 3 : Differentiability at $$x=1$$

The point $$x=1$$ lies in the region $$x\le 2$$, so in a neighbourhood of 1 the definition is simply $$f(x)=5x+1$$. Since a linear function has a constant derivative 5 everywhere, $$f(x)$$ is certainly differentiable at $$x=1$$.

Step 4 : Collecting the facts

We have shown that

• $$f(x)$$ is continuous at $$x=2$$,
• but it is not differentiable at $$x=2$$ (the derivatives from the two sides differ),
• and $$f(x)$$ is differentiable at $$x=1$$.

Thus the function is “continuous but not differentiable at $$x=2$$.’’ This matches Option C.

Hence, the correct answer is Option C.

We are given that $$f$$ is twice differentiable on $$\mathbb{R}$$ with $$f(0) = 1$$, $$f'(0) = 2$$, $$f'(x) \neq 0$$ for all $$x$$, and $$\begin{vmatrix} f(x) & f'(x) \\ f'(x) & f''(x) \end{vmatrix} = 0$$ for all $$x$$.

Expanding the determinant gives $$f(x) \cdot f''(x) - [f'(x)]^2 = 0$$, which can be rewritten as $$\frac{f(x) \cdot f''(x) - [f'(x)]^2}{[f(x)]^2} = 0$$.

This is exactly $$\frac{d}{dx}\left(\frac{f'(x)}{f(x)}\right) = 0$$. Therefore, $$\frac{f'(x)}{f(x)} = k$$ for some constant $$k$$.

Using the initial conditions, $$k = \frac{f'(0)}{f(0)} = \frac{2}{1} = 2$$. So $$\frac{f'(x)}{f(x)} = 2$$, which gives $$\frac{d}{dx}[\ln|f(x)|] = 2$$.

Integrating, $$\ln|f(x)| = 2x + C_1$$, so $$f(x) = Ce^{2x}$$. Using $$f(0) = 1$$, we get $$C = 1$$, and therefore $$f(x) = e^{2x}$$.

Now, $$f(1) = e^2 \approx 7.389$$, which lies in the interval $$(6, 9)$$.

Therefore, the value of $$f(1)$$ lies in the interval $$(6, 9)$$.

For $$-2 \leq x \leq 2$$, we have $$f(x) = \min\{|x|, 2 - x^2\}$$. Setting $$|x| = 2 - x^2$$ gives $$x^2 + |x| - 2 = 0$$, so $$|x| = 1$$, meaning $$x = \pm 1$$. For $$|x| < 1$$: at $$x = 0$$, $$|x| = 0 < 2 = 2 - x^2$$, so $$f(x) = |x|$$. For $$1 < |x| < 2$$: at $$x = 1.5$$, $$|x| = 1.5 > 2 - 2.25 = -0.25$$, so $$f(x) = 2 - x^2$$.

For $$2 < |x| \leq 3$$, $$f(x) = [|x|]$$ (greatest integer function). So for $$2 < x \leq 3$$, $$f(x) = [x] = 2$$, and for $$-3 \leq x < -2$$, $$f(x) = [|x|] = 2$$.

Now we identify points of non-differentiability in $$(-3, 3)$$:

At $$x = 0$$: $$f(x) = |x|$$ has a corner (left derivative $$= -1$$, right derivative $$= 1$$), so $$f$$ is not differentiable.

At $$x = 1$$: for $$x < 1$$, $$f(x) = x$$ with derivative 1. For $$x > 1$$, $$f(x) = 2 - x^2$$ with derivative $$-2x = -2$$. Since $$1 \neq -2$$, not differentiable. Similarly at $$x = -1$$: left derivative of $$2-x^2$$ is $$-2(-1) = 2$$, right derivative of $$|x| = -x$$ is $$-1$$. Not differentiable.

At $$x = 2$$: $$f(2) = \min\{2, -2\} = -2$$ from the left, but $$f(x) = [x] = 2$$ for $$x$$ just above 2. Since $$f(2^-) = -2 \neq 2 = f(2^+)$$, there is a discontinuity, hence not differentiable.

At $$x = -2$$: similarly $$f(-2) = \min\{2, -2\} = -2$$ and $$f(x) = 2$$ for $$x$$ just below $$-2$$. Discontinuity, hence not differentiable.

No other points of non-differentiability exist (the greatest integer function $$[|x|] = 2$$ is constant on $$(2, 3)$$ and $$(-3, -2)$$, so it is differentiable there).

The total number of points of non-differentiability is $$5$$.

We have the function defined as $$f(x)=\dfrac{P(x)}{\sin\,(x-2)} \quad\text{for }x\neq 2$$ and $$f(2)=7.$$

Because the question states that $$f(x)$$ is continuous at $$x=2$$, the limit of the first formula as $$x\to 2$$ must equal the explicitly given value at that point. Hence we require

$$\lim_{x\to 2}\dfrac{P(x)}{\sin\,(x-2)} \;=\;7.$$

Next we use the standard limit fact $$\displaystyle\lim_{u\to 0}\frac{\sin u}{u}=1,$$ which can be rewritten (by taking reciprocals) as $$\displaystyle\lim_{u\to 0}\frac{u}{\sin u}=1.$$ Writing $$u = x-2,$$ we see that $$u\to 0$$ exactly when $$x\to 2.$$ Therefore near $$x=2$$ we may replace $$\sin (x-2)$$ by $$(x-2)$$ inside limits. It follows that, to keep the fraction finite, the numerator must also vanish at $$x=2.$$ So we must have

$$P(2)=0.$$

With $$P(2)=0$$ established, both numerator and denominator approach $$0$$ in the limit, so L’Hospital’s Rule may be applied. L’Hospital’s Rule states that if $$\displaystyle\lim_{x\to a} \dfrac{g(x)}{h(x)}$$ is an indeterminate form $$0/0,$$ then

$$\lim_{x\to a}\dfrac{g(x)}{h(x)}=\lim_{x\to a}\dfrac{g'(x)}{h'(x)},$$

provided the latter limit exists. Using $$g(x)=P(x)$$ and $$h(x)=\sin(x-2),$$ we obtain

$$\lim_{x\to 2}\dfrac{P(x)}{\sin (x-2)}=\lim_{x\to 2}\dfrac{P'(x)}{\cos (x-2)}.$$

Since $$\cos(0)=1,$$ the right-hand limit simplifies to $$P'(2).$$ Continuity therefore forces

$$P'(2)=7.$$

The problem also states that $$P''(x)$$ is a constant for all $$x.$$ A constant second derivative implies that $$P(x)$$ must be a quadratic polynomial. Let us write

$$P''(x)=k,\qquad k\text{ constant}.$$

Integrating once,

$$P'(x)=kx+d,$$

where $$d$$ is a constant of integration. Substituting $$x=2$$ and using $$P'(2)=7$$ gives

$$k\cdot 2+d=7\quad\Longrightarrow\quad 2k+d=7. \quad -(1)$$

Integrating $$P'(x)$$ again yields

$$P(x)=\frac{k}{2}x^{2}+dx+e,$$

with a second integration constant $$e.$$ Using the already-proved fact $$P(2)=0$$ we substitute $$x=2$$ to get

$$\frac{k}{2}\,(2)^{2}+d\,(2)+e=0 \;\Longrightarrow\; 2k+2d+e=0. \quad -(2)$$

We are additionally told that $$P(3)=9.$$ Substituting $$x=3$$ gives

$$\frac{k}{2}\,(3)^{2}+d\,(3)+e=9 \;\Longrightarrow\; \frac{9k}{2}+3d+e=9. \quad -(3)$$

Now we solve the simultaneous linear equations (1), (2) and (3).

From (1) we can express $$d$$ directly:

$$d=7-2k.$$

Substituting this value of $$d$$ into (2) gives

$$2k+2(7-2k)+e=0 \;\Longrightarrow\; 2k+14-4k+e=0 \;\Longrightarrow\; -2k+14+e=0 \;\Longrightarrow\; e=2k-14.$$

Next we insert both $$d=7-2k$$ and $$e=2k-14$$ into equation (3):

$$\frac{9k}{2}+3(7-2k)+(2k-14)=9.$$

Performing the algebra step by step,

$$\frac{9k}{2}+21-6k+2k-14=9,$$

which simplifies to

$$\frac{9k}{2}-4k+7=9.$$

Combining the $$k$$ terms by writing $$-4k=-\dfrac{8k}{2},$$ we get

$$\frac{9k}{2}-\frac{8k}{2}+7=9 \;\Longrightarrow\; \frac{k}{2}+7=9 \;\Longrightarrow\; \frac{k}{2}=2 \;\Longrightarrow\; k=4.$$

With $$k=4,$$ we quickly find the remaining constants:

$$d=7-2k=7-8=-1,$$

$$e=2k-14=8-14=-6.$$

Therefore the explicit quadratic polynomial is

$$P(x)=\frac{4}{2}x^{2}-x-6=2x^{2}-x-6.$$

Finally we compute $$P(5):$$

$$P(5)=2(5)^{2}-5-6=2\cdot25-5-6=50-5-6=39.$$

So, the answer is $$39$$.

We are given the real-valued function

$$f(x)= \begin{cases} a\sin\left(\dfrac{\pi}{2}(x-1)\right), & x\le 0\\[6pt] \dfrac{\tan 2x-\sin 2x}{b\,x^{3}}, & x\gt0 \end{cases}$$

and we know that $$b\neq 0$$. For continuity at $$x=0$$ we must have

$$\lim_{x\to 0^-}f(x)=f(0)=\lim_{x\to 0^+}f(x).$$

Left-hand value and limit

Because the first branch is defined for $$x\le 0$$, the value of the function at the point itself is obtained from that branch:

$$f(0)=a\sin\left(\frac{\pi}{2}(0-1)\right)=a\sin\left(-\frac{\pi}{2}\right).$$

Using $$\sin(-\theta)=-\sin\theta$$ and the fact that $$\sin\frac{\pi}{2}=1$$, we get

$$f(0)=a(-1)=-a.$$

Since the formula is the same for all $$x\le 0$$, the left-hand limit as $$x\to 0^-$$ is also $$-a$$.

Right-hand limit

For $$x\gt0$$ the function is

$$f(x)=\frac{\tan 2x-\sin 2x}{b\,x^{3}}.$$ To find $$\displaystyle\lim_{x\to 0^+}f(x)$$, we expand the numerator in powers of $$x$$ (Maclaurin series).

Standard Maclaurin series (stated first):

$$\sin\theta=\theta-\frac{\theta^{3}}{6}+O(\theta^{5}),\qquad \tan\theta=\theta+\frac{\theta^{3}}{3}+O(\theta^{5}).$$

Now substitute $$\theta=2x$$.

We have $$$ \begin{aligned} \tan 2x &= 2x+\frac{(2x)^{3}}{3}+O(x^{5}) = 2x+\frac{8x^{3}}{3}+O(x^{5}),\\[4pt] \sin 2x &= 2x-\frac{(2x)^{3}}{6}+O(x^{5}) = 2x-\frac{8x^{3}}{6}+O(x^{5}) = 2x-\frac{4x^{3}}{3}+O(x^{5}). \end{aligned} $$$

Subtracting term by term:

$$\tan 2x-\sin 2x =\bigl(2x+\frac{8x^{3}}{3}\bigr)-\bigl(2x-\frac{4x^{3}}{3}\bigr)+O(x^{5}) =(2x-2x)+\frac{8x^{3}}{3}+\frac{4x^{3}}{3}+O(x^{5}) =4x^{3}+O(x^{5}).$$

Therefore, near $$x=0$$,

$$\tan 2x-\sin 2x \;=\;4x^{3}+O(x^{5}).$$

Substituting this into the expression for $$f(x)$$ when $$x\gt0$$, we obtain

$$f(x)=\frac{4x^{3}+O(x^{5})}{b\,x^{3}} =\frac{4}{b}+O(x^{2}).$$

Hence

$$\lim_{x\to 0^+}f(x)=\frac{4}{b}.$$

Imposing continuity

Continuity at $$x=0$$ requires

$$-a=\frac{4}{b}.$$

Rewriting, we get

$$ab=-4.$$

We are asked to evaluate $$10-ab$$. Substituting $$ab=-4$$ gives

$$10-ab=10-(-4)=14.$$

So, the answer is $$14$$.

We have the function $$f:[0,3]\to\mathbb R$$ given by

$$f(x)=\min\{x-[x],\;1+[x]-x\},$$

where $$[x]$$ denotes the greatest integer less than or equal to $$x$$. For each integer $$n$$ with $$0\le n\le2$$, every point $$x$$ in the sub-interval $$[n,n+1)$$ satisfies $$[x]=n$$, so we may write

$$x-[x]=x-n\quad\text{and}\quad 1+[x]-x = 1+n-x.$$

If we introduce the fractional part $$\{x\}=x-n\;(0\le\{x\}<1)$$, then inside the same sub-interval we obtain the much simpler expression

$$f(x)=\min\{\{x\},\;1-\{x\}\}.$$

Now $$\{x\}$$ increases linearly from $$0$$ to $$1$$ while $$1-\{x\}$$ decreases linearly from $$1$$ to $$0$$. The smaller of the two is therefore

$$\{x\}\quad\text{when}\quad\{x\}\le\frac12,\qquad\text{and}\qquad1-\{x\}\quad\text{when}\quad\{x\}\ge\frac12.$$

Hence on each open unit interval $$(n,n+1)$$ the function assumes the piece-wise linear form

$$ f(x)= \begin{cases} \{x\}, & 0\le\{x\}\le\dfrac12,\\\\ 1-\{x\}, & \dfrac12\le\{x\}<1. \end{cases} $$

Continuity is checked first. At a non-end-point $$x$$ lying strictly between two consecutive integers, $$f$$ is given by one of the linear formulas above, so it is continuous there. At an integer $$k\;(k=0,1,2,3)$$ we have

$$\lim_{x\to k^-}f(x)=0,\qquad\lim_{x\to k^+}f(x)=0,$$

while directly from the definition

$$f(k)=\min\{k-k,\;1+k-k\}=0.$$

Since the left limit, the right limit and the value of the function coincide, $$f$$ is continuous at every integer as well. Thus the set

$$P=\{x\in[0,3]\mid f\text{ is discontinuous at }x\}$$

is empty, so $$|P|=0.$$

We now investigate differentiability. Inside each open interval $$(n,n+1)$$ we already have linear pieces, so the derivative exists there and equals

$$f'(x)= \begin{cases} 1, & 0<\{x\}<\dfrac12,\\\\ -1, & \dfrac12<\{x\}<1. \end{cases} $$

Possible trouble points are where these two formulas meet, namely where $$\{x\}=\dfrac12$$, and also the integers where two adjacent unit intervals meet.

(i) Points with fractional part ½.
Solving $$\{x\}=\dfrac12$$ in each interval $$(n,n+1)$$ gives $$x=n+\dfrac12.$$ Within the domain $$[0,3]$$ this yields the three points

$$x=0.5,\;1.5,\;2.5.$$

At each of them the left derivative equals $$1$$ while the right derivative equals $$-1$$, so $$f$$ is not differentiable there.

(ii) Integer points.
At an integer $$k$$ the left derivative (coming from the slope $$-1$$ of the segment that ends at $$x=k$$) equals $$-1$$, whereas the right derivative (coming from the slope $$1$$ of the segment that starts at $$x=k$$) equals $$1$$. Therefore $$f$$ fails to be differentiable at every integer.

All integers in our closed interval are $$0,1,2,3$$, but the set

$$Q=\{x\in(0,3)\mid f\text{ is not differentiable at }x\}$$

excludes the endpoints $$0$$ and $$3$$. Consequently only $$1$$ and $$2$$ from the list above belong to $$Q$$.

Collecting everything lying strictly between $$0$$ and $$3$$, the non-differentiable points are

$$1,\;2,\;0.5,\;1.5,\;2.5,$$

so $$|Q|=5.$$

Finally, the required sum is

$$|P|+|Q| = 0 + 5 = 5.$$

Hence, the correct answer is Option 5.

We need $$g(f(x))$$ to be continuous for all $$x \in R$$. First, note that $$f(x) = x + a$$ for $$x < 0$$ and $$f(x) = |x-1|$$ for $$x \geq 0$$.

For $$x < 0$$: $$f(x) = x + a$$. If $$a \geq 0$$, then as $$x \to 0^-$$, $$f(x) \to a \geq 0$$. For $$x$$ sufficiently negative, $$f(x) < 0$$. The transition happens at $$x = -a$$.

For $$x < -a$$: $$f(x) = x + a < 0$$, so $$g(f(x)) = f(x) + 1 = x + a + 1$$. For $$-a \leq x < 0$$: $$f(x) = x + a \geq 0$$, so $$g(f(x)) = (f(x) - 1)^2 + b = (x+a-1)^2 + b$$. For $$x \geq 0$$: $$f(x) = |x-1| \geq 0$$, so $$g(f(x)) = (|x-1|-1)^2 + b$$.

Checking continuity at $$x = -a$$: From the left, $$g(f(-a^-)) = -a + a + 1 = 1$$. From the right, $$g(f(-a^+)) = (-a + a - 1)^2 + b = 1 + b$$. For continuity: $$1 = 1 + b$$, so $$b = 0$$.

Checking continuity at $$x = 0$$: From the left (with $$-a \leq x < 0$$), $$g(f(0^-)) = (0 + a - 1)^2 + b = (a-1)^2$$. From the right, $$g(f(0^+)) = (|0-1|-1)^2 + b = (1-1)^2 + 0 = 0$$. For continuity: $$(a-1)^2 = 0$$, so $$a = 1$$.

Therefore $$a + b = 1 + 0 = 1$$.

The answer is $$1$$.

We have $$f(x) = |2x + 1| - 3|x + 2| + |x^2 + x - 2|$$. Note that $$x^2 + x - 2 = (x + 2)(x - 1)$$, so $$|x^2 + x - 2| = |x + 2||x - 1|$$.

The critical points where the expressions inside the absolute values change sign are $$x = -\frac{1}{2}$$ (from $$|2x+1|$$), $$x = -2$$ (from $$|x+2|$$), and $$x = 1$$ (from $$|x-1|$$).

We analyze each interval and check differentiability at each critical point.

For $$x < -2$$: $$|2x+1| = -(2x+1)$$, $$|x+2| = -(x+2)$$, $$|x+2||x-1| = (-(x+2))(-(x-1)) = (x+2)(x-1)$$. So $$f(x) = -(2x+1) + 3(x+2) + (x+2)(x-1) = -2x - 1 + 3x + 6 + x^2 + x - 2 = x^2 + 2x + 3$$.

For $$-2 < x < -\frac{1}{2}$$: $$|2x+1| = -(2x+1)$$, $$|x+2| = x+2$$, $$|x+2||x-1| = (x+2)(-(x-1)) = -(x+2)(x-1)$$. So $$f(x) = -(2x+1) - 3(x+2) - (x+2)(x-1) = -2x - 1 - 3x - 6 - x^2 - x + 2 = -x^2 - 6x - 5$$.

At $$x = -2$$: Left derivative from $$x^2 + 2x + 3$$ is $$2(-2) + 2 = -2$$. Right derivative from $$-x^2 - 6x - 5$$ is $$-2(-2) - 6 = -2$$. Both equal $$-2$$, so $$f$$ is differentiable at $$x = -2$$.

For $$-\frac{1}{2} < x < 1$$: $$|2x+1| = 2x+1$$, $$|x+2| = x+2$$, $$|x+2||x-1| = (x+2)(1-x)$$. So $$f(x) = (2x+1) - 3(x+2) + (x+2)(1-x) = 2x + 1 - 3x - 6 - x^2 - x + 2 = -x^2 - 2x - 3$$.

At $$x = -\frac{1}{2}$$: Left derivative from $$-x^2 - 6x - 5$$ is $$-2(-\frac{1}{2}) - 6 = -5$$. Right derivative from $$-x^2 - 2x - 3$$ is $$-2(-\frac{1}{2}) - 2 = -1$$. Since $$-5 \neq -1$$, $$f$$ is not differentiable at $$x = -\frac{1}{2}$$.

For $$x > 1$$: $$|2x+1| = 2x+1$$, $$|x+2| = x+2$$, $$|x+2||x-1| = (x+2)(x-1)$$. So $$f(x) = (2x+1) - 3(x+2) + (x+2)(x-1) = 2x + 1 - 3x - 6 + x^2 + x - 2 = x^2 - 7$$.

At $$x = 1$$: Left derivative from $$-x^2 - 2x - 3$$ is $$-2(1) - 2 = -4$$. Right derivative from $$x^2 - 7$$ is $$2(1) = 2$$. Since $$-4 \neq 2$$, $$f$$ is not differentiable at $$x = 1$$.

Therefore, the number of points where $$f$$ is not differentiable is $$2$$.

Let $$h(t) = t^3 - 6t^2 + 9t - 3$$. We find its critical points: $$h'(t) = 3t^2 - 12t + 9 = 3(t-1)(t-3)$$. So $$h$$ has a local maximum at $$t=1$$ with $$h(1) = 1 - 6 + 9 - 3 = 1$$, a local minimum at $$t=3$$ with $$h(3) = 27 - 54 + 27 - 3 = -3$$, and $$h(0) = -3$$.

For $$0 \le x \le 3$$, $$g(x) = \max_{0 \le t \le x} h(t)$$. We track how this running maximum evolves as $$x$$ increases from 0 to 3.

At $$x=0$$: $$g(0) = h(0) = -3$$.

For $$0 < x \le 1$$: $$h$$ is increasing (since $$h'(t) > 0$$ on $$(0,1)$$), so the maximum on $$[0,x]$$ is $$h(x)$$. Thus $$g(x) = h(x)$$ on $$(0,1]$$.

For $$1 < x \le 3$$: $$h$$ decreases from $$h(1)=1$$ to $$h(3)=-3$$. The maximum on $$[0,x]$$ is still $$h(1) = 1$$. Thus $$g(x) = 1$$ on $$(1,3]$$.

For $$3 < x \le 4$$: $$g(x) = 4 - x$$.

Now we check differentiability at each transition point in $$(0,4)$$:

At $$x = 1$$: For $$x \le 1$$, $$g(x) = h(x)$$, so $$g'(1^-) = h'(1) = 0$$. For $$x > 1$$, $$g(x) = 1$$, so $$g'(1^+) = 0$$. Both one-sided derivatives equal 0, so $$g$$ is differentiable at $$x=1$$.

At $$x = 3$$: For $$x \le 3$$, $$g(x) = 1$$, so $$g'(3^-) = 0$$. For $$x > 3$$, $$g(x) = 4-x$$, so $$g'(3^+) = -1$$. Since $$0 \neq -1$$, $$g$$ is NOT differentiable at $$x = 3$$.

We also check $$x = 0$$ (the running maximum): at $$x = 0$$, $$h(0) = -3$$ is a local min, but the maximum function starts equalling $$h(x)$$ immediately and $$h'(0) = 9 > 0$$, so no issue there for $$x \in (0,4)$$.

Therefore, the number of points in $$(0, 4)$$ where $$g$$ is not differentiable is $$\boxed{1}$$.

The function $$f(x) = \begin{cases} 3\left(1 - \frac{|x|}{2}\right) & \text{if } |x| \le 2 \\ 0 & \text{if } |x| > 2 \end{cases}$$ is a triangular function with peak value 3 at $$x = 0$$, decreasing linearly to 0 at $$x = \pm 2$$.

We can write $$f$$ piecewise as: $$f(x) = 0$$ for $$x < -2$$; $$f(x) = 3 + \frac{3x}{2}$$ for $$-2 \le x \le 0$$; $$f(x) = 3 - \frac{3x}{2}$$ for $$0 \le x \le 2$$; $$f(x) = 0$$ for $$x > 2$$.

Now $$g(x) = f(x+2) - f(x-2)$$. The function $$f(x+2)$$ is nonzero when $$|x+2| \le 2$$, i.e., $$-4 \le x \le 0$$. The function $$f(x-2)$$ is nonzero when $$|x-2| \le 2$$, i.e., $$0 \le x \le 4$$.

Computing $$f(x+2)$$ piecewise: For $$-4 \le x \le -2$$, we have $$x + 2 \in [-2, 0]$$, so $$f(x+2) = 3 + \frac{3(x+2)}{2} = 6 + \frac{3x}{2}$$. For $$-2 \le x \le 0$$, we have $$x + 2 \in [0, 2]$$, so $$f(x+2) = 3 - \frac{3(x+2)}{2} = -\frac{3x}{2}$$.

Computing $$f(x-2)$$ piecewise: For $$0 \le x \le 2$$, we have $$x - 2 \in [-2, 0]$$, so $$f(x-2) = 3 + \frac{3(x-2)}{2} = \frac{3x}{2}$$. For $$2 \le x \le 4$$, we have $$x - 2 \in [0, 2]$$, so $$f(x-2) = 3 - \frac{3(x-2)}{2} = 6 - \frac{3x}{2}$$.

Therefore $$g(x)$$ is: $$g(x) = 0$$ for $$x < -4$$; $$g(x) = 6 + \frac{3x}{2}$$ for $$-4 \le x \le -2$$; $$g(x) = -\frac{3x}{2}$$ for $$-2 \le x \le 0$$; $$g(x) = -\frac{3x}{2}$$ for $$0 \le x \le 2$$; $$g(x) = -6 + \frac{3x}{2}$$ for $$2 \le x \le 4$$; $$g(x) = 0$$ for $$x > 4$$.

Notice that on $$[-2, 2]$$, $$g(x) = -\frac{3x}{2}$$ is a single linear piece, so $$g$$ is smooth there (including at $$x = 0$$).

Checking continuity at each breakpoint: At $$x = -4$$: left limit is 0 and $$g(-4) = 6 - 6 = 0$$. Continuous. At $$x = -2$$: left value $$= 6 - 3 = 3$$ and right value $$= 3$$. Continuous. At $$x = 0$$: both sides give 0. Continuous. At $$x = 2$$: left value $$= -3$$ and right value $$= -6 + 3 = -3$$. Continuous. At $$x = 4$$: left value $$= -6 + 6 = 0$$ and right value $$= 0$$. Continuous.

So $$g$$ is continuous everywhere, meaning $$n = 0$$.

Checking differentiability: At $$x = -4$$: left derivative is 0, right derivative is $$\frac{3}{2}$$. Not differentiable. At $$x = -2$$: left derivative is $$\frac{3}{2}$$, right derivative is $$-\frac{3}{2}$$. Not differentiable. At $$x = 0$$: both sides have derivative $$-\frac{3}{2}$$. Differentiable. At $$x = 2$$: left derivative is $$-\frac{3}{2}$$, right derivative is $$\frac{3}{2}$$. Not differentiable. At $$x = 4$$: left derivative is $$\frac{3}{2}$$, right derivative is 0. Not differentiable.

So $$g$$ is not differentiable at 4 points: $$x = -4, -2, 2, 4$$, giving $$m = 4$$.

Therefore $$n + m = 0 + 4 = 4$$.

Let us remember the definition: for any real number $$t$$ the symbol $$[t]$$ denotes “the greatest integer less than or equal to $$t$$.” The function to be studied is

$$f(x)= [x]\;|x^{2}-1|+\sin\!\left(\dfrac{\pi}{[x]+3}\right)-[x+1],\qquad x\in(-2,2).$$

The only positions where discontinuity can occur are the points at which at least one of the three component expressions $$[x]$$, $$|x^{2}-1|$$ or $$[x+1]$$ changes its algebraic description. The absolute-value term $$|x^{2}-1|$$ is continuous everywhere, so we only need to watch where the greatest-integer symbols change value, i.e. at integer values of $$x$$. Inside the open interval $$(-2,2)$$ those integers are $$x=-1,\;0,\;1.$$

We therefore study the function separately on the four open sub-intervals determined by these integers.

1. Interval $$(-2,-1)$$

Here we have $$[x]=-2.$$ Therefore $$[x]+3=1$$ and $$\sin\!\left(\dfrac{\pi}{[x]+3}\right)=\sin(\pi)=0.$$ Further, $$x+1\in(-1,0)$$ so $$[x+1]=-1.$$ Substituting these three results gives

$$f(x)=(-2)\,|x^{2}-1|+0-(-1)= -2|x^{2}-1|+1.$$

2. Interval $$(-1,0)$$

Now $$[x]=-1,$$ whence $$[x]+3=2$$ and $$\sin\!\left(\dfrac{\pi}{[x]+3}\right)=\sin\!\left(\dfrac{\pi}{2}\right)=1.$$ Also $$x+1\in(0,1)$$ so $$[x+1]=0.$$ Hence

$$f(x)=(-1)\,|x^{2}-1|+1-0= -|x^{2}-1|+1.$$

3. Interval $$(0,1)$$

Here $$[x]=0,$$ giving $$[x]+3=3$$ and $$\sin\!\left(\dfrac{\pi}{[x]+3}\right)=\sin\!\left(\dfrac{\pi}{3}\right)=\dfrac{\sqrt3}{2}.$$ Also $$x+1\in(1,2)$$ so $$[x+1]=1.$$ Therefore

$$f(x)=0\cdot|x^{2}-1|+\dfrac{\sqrt3}{2}-1=\dfrac{\sqrt3}{2}-1,$$

a constant on this whole sub-interval.

4. Interval $$(1,2)$$

Now $$[x]=1,$$ so $$[x]+3=4$$ and $$\sin\!\left(\dfrac{\pi}{[x]+3}\right)=\sin\!\left(\dfrac{\pi}{4}\right)=\dfrac{\sqrt2}{2}.$$ Moreover $$x+1\in(2,3)$$ hence $$[x+1]=2.$$ We obtain

$$f(x)=1\cdot|x^{2}-1|+\dfrac{\sqrt2}{2}-2=|x^{2}-1|+\dfrac{\sqrt2}{2}-2.$$

Within each open sub-interval the formula is built only from continuous pieces (constants, the continuous absolute value, and simple arithmetic), so $$f(x)$$ is continuous there. We now examine the three candidate points one by one.

Point $$x=-1$$

Left-hand limit (using the $$(-2,-1)$$ formula):

$$\lim_{x\to-1^-}f(x)= -2|(-1)^{2}-1|+1=-2\cdot0+1=1.$$

Right-hand limit (using the $$(-1,0)$$ formula):

$$\lim_{x\to-1^+}f(x)= -|(-1)^{2}-1|+1=-0+1=1.$$

Value of the function at $$x=-1$$:

$$f(-1)=(-1)\cdot0+\sin\!\left(\dfrac{\pi}{2}\right)-[0]=0+1-0=1.$$

Both limits equal the function value, hence $$f(x)$$ is continuous at $$x=-1.$$

Point $$x=0$$

Left-hand limit (use $$(-1,0)$$):

$$\lim_{x\to0^-}f(x)= -|0^{2}-1|+1=-(1)+1=0.$$

Right-hand limit (use $$(0,1)$$, which is constant):

$$\lim_{x\to0^+}f(x)=\dfrac{\sqrt3}{2}-1.$$

Since $$0\neq\dfrac{\sqrt3}{2}-1,$$ the two one-sided limits are different, so the function jumps here. Consequently $$f(x)$$ is not continuous at $$x=0$$ (even though $$f(0)=\dfrac{\sqrt3}{2}-1$$ equals the right limit).

Point $$x=1$$

Left-hand limit (use $$(0,1)$$, constant):

$$\lim_{x\to1^-}f(x)=\dfrac{\sqrt3}{2}-1.$$

Right-hand limit (use $$(1,2)$$):

$$\lim_{x\to1^+}f(x)=|1^{2}-1|+\dfrac{\sqrt2}{2}-2=0+\dfrac{\sqrt2}{2}-2.$$

Because $$\dfrac{\sqrt3}{2}-1\neq\dfrac{\sqrt2}{2}-2,$$ the one-sided limits differ, giving another jump. Hence $$f(x)$$ is discontinuous at $$x=1$$ (again the actual value $$f(1)=\dfrac{\sqrt2}{2}-2$$ matches only the right limit).

There are no other integers inside the open interval $$(-2,2),$$ so the complete list of discontinuities is $$\{0,\,1\}.$$ Thus the number of points of discontinuity is $$2.$$

So, the answer is $$2.$$

Condition for Continuity

For the function$$f(x)$$ to be continuous at $$x = 0$$, the following condition must be satisfied:

$$\lim_{x \to 0^-} f(x) = f(0) = \lim_{x \to 0^+} f(x)$$

1. Evaluation of the Left Hand Limit (LHL)

Using the piece defined for $$x < 0$$:

$$\text{LHL} = \lim_{x \to 0^-} \left( \frac{\sin(a+2)x + \sin x}{x} \right)$$

We can split this into two separate limits:

$$\text{LHL} = \lim_{x \to 0^-} \frac{\sin(a+2)x}{x} + \lim_{x \to 0^-} \frac{\sin x}{x}$$

Using the standard trigonometric limit $$\lim_{\theta \to 0} \frac{\sin(k\theta)}{\theta} = k$$, we get:

$$LHL\ =\ \left(a+2\right)\ +\ 1$$

$$LHL\ =\ a+3$$

2. Evaluation of the Right Hand Limit (RHL)

Using the piece defined for $$x > 0$$:

$$\text{RHL} = \lim_{x \to 0^+} \frac{(x + 3x^2)^{1/3} - x^{1/3}}{x^{4/3}}$$

Factor $x^{1/3}$ out of the numerator to simplify:

$$\text{RHL} = \lim_{x \to 0^+} \frac{x^{1/3} \left[ (1 + 3x)^{1/3} - 1 \right]}{x^{4/3}} = \lim_{x \to 0^+} \frac{(1 + 3x)^{1/3} - 1}{x}$$

Applying the binomial approximation $$\left(1+z\right)^n\approx\ 1+nz\ for\ z\longrightarrow\ 0:$$:

$$\text{RHL} = \lim_{x \to 0^+} \frac{\left( 1 + \frac{1}{3}(3x) \right) - 1}{x} = \lim_{x \to 0^+} \frac{x}{x} = 1$$

3. Solving for $$a$$ and $$b$$

Since $$f(0) = b$$, we equate the LHL and RHL to $$b$$:

• From RHL: $$b = 1$$
• From LHL: $$a + 3 = b \implies a + 3 = 1 \implies a = -2$$

Final Result

The problem asks for the value of $$a + 2b$$:

$$a + 2b = (-2) + 2(1) = 0$$

We are given the real-valued function $$f:\mathbb R\to\mathbb R$$ defined by $$f(x)=\max\{x,\;x^2\}\,.$$

To analyse differentiability we first express $$f$$ as a piece-wise function, because at each real number we must decide which of the two expressions, $$x$$ or $$x^2$$, is larger.

We compare $$x^2$$ with $$x$$:

$$x^2\ge x\;\Longleftrightarrow\;x^2-x\ge0\;\Longleftrightarrow\;x(x-1)\ge0.$$

The inequality $$x(x-1)\ge0$$ holds when $$x\le0$$ or $$x\ge1$$, and it fails when $$0<x<1$$. Hence

$$ f(x)= \begin{cases} x^2,& x\le0,\\[4pt] x, & 0\lt x\lt 1,\\[4pt] x^2,& x\ge1. \end{cases} $$

Now we differentiate each branch separately.

For $$x<0$$ we have $$f(x)=x^2,$$ so using the standard rule $$\dfrac{d}{dx}(x^n)=nx^{n-1}$$ we get

$$f'(x)=2x\qquad(x<0).$$

For $$0<x<1$$ we have $$f(x)=x,$$ and the derivative of $$x$$ is

$$f'(x)=1\qquad(0<x<1).$$

For $$x>1$$ we have again $$f(x)=x^2,$$ giving

$$f'(x)=2x\qquad(x>1).$$

Thus $$f'$$ is well defined everywhere except possibly at the junction points $$x=0$$ and $$x=1$$. We must examine these two points separately by comparing the left-hand and right-hand derivatives.

Point $$x=0$$.

The left-hand derivative is the limit of $$2x$$ as $$x\to0^-$$:

$$\lim_{x\to0^-}2x=0.$$

The right-hand derivative is the limit of $$1$$ as $$x\to0^+$$:

$$\lim_{x\to0^+}1=1.$$

Because $$0\ne1$$, the two one-sided derivatives are unequal, so $$f$$ is not differentiable at $$x=0$$.

Point $$x=1$$.

The left-hand derivative is the limit of $$1$$ as $$x\to1^-$$:

$$\lim_{x\to1^-}1=1.$$

The right-hand derivative is the limit of $$2x$$ as $$x\to1^+$$:

$$\lim_{x\to1^+}2x=2.$$

Since $$1\ne2$$, the one-sided derivatives differ, so $$f$$ is not differentiable at $$x=1$$.

For every other real number the function matches just one smooth branch, and the derivative we calculated is finite and continuous, hence $$f$$ is differentiable everywhere except at $$0$$ and $$1$$.

Therefore the set $$S$$ of non-differentiability points is

$$S=\{0,1\}.$$

Among the given options, this set corresponds to Option A.

Hence, the correct answer is Option A.

We have the piece‐wise definition

$$f(x)=\begin{cases} ae^{x}+be^{-x}, & -1\le x<1\\[4pt] cx^{2}, & 1\le x\le3\\[4pt] ax^{2}+2cx, & 3<x\le4 \end{cases}$$

Because the question says that $$f(x)$$ is continuous everywhere in its domain, the left-hand and right-hand limits at the points where the rule changes must be equal to the actual function value. Thus we must impose continuity at $$x=1$$ and at $$x=3$$.

At $$x=1$$, the value coming from the first branch is

$$f(1^-)=ae^{1}+be^{-1}=ae+ \frac{b}{e}.$$

The value given by the second branch is

$$f(1^+)=c\,(1)^2=c.$$

Equating these two for continuity, we get

$$ae+\frac{b}{e}=c\qquad\qquad (1).$$

At $$x=3$$, the value from the second branch is

$$f(3^-)=c\,(3)^2=9c,$$

while the value from the third branch is

$$f(3^+)=a\,(3)^2+2c\,(3)=9a+6c.$$

Equality of these two expressions gives

$$9c=9a+6c.$$

Simplifying,

$$9c-6c=9a\;\;\Longrightarrow\;\;3c=9a\;\;\Longrightarrow\;\;c=3a\qquad\qquad (2).$$

Now we substitute $$c=3a$$ into equation (1):

$$ae+\frac{b}{e}=3a.$$

Isolating $$b$$, we write

$$\frac{b}{e}=3a-ae\;\;\Longrightarrow\;\;b=e\bigl(3a-ae\bigr)=ae(3-e)\qquad\qquad (3).$$

Next we turn to the derivative. For each interval we differentiate the corresponding expression.

• For $$-1<x<1$$ we have $$f(x)=ae^{x}+be^{-x}$$, so

$$f'(x)=ae^{x}-be^{-x}.$$

• For $$1<x<3$$ we have $$f(x)=cx^{2}$$, so

$$f'(x)=2cx.$$

• For $$3<x\le4$$ we have $$f(x)=ax^{2}+2cx$$, so

$$f'(x)=2ax+2c.$$

Therefore

$$f'(0)=ae^{0}-be^{0}=a-b,$$

because $$e^{0}=1.$$

Also, $$2$$ lies in the interval $$1\le x\le3,$$ so we use the middle derivative:

$$f'(2)=2c\,(2)=4c.$$

The problem tells us that

$$f'(0)+f'(2)=e.$$

Substituting the expressions just found,

$$(a-b)+4c=e.$$

Now we insert the relations (2) and (3): $$c=3a$$ and $$b=ae(3-e).$$

Thus

$$(a-ae(3-e))+4(3a)=e.$$

First combine like terms:

$$a-ae(3-e)+12a=e.$$

Notice that $$a+12a=13a,$$ so

$$13a-ae(3-e)=e.$$

Factor out $$a$$ from the left‐hand side:

$$a\bigl(13-e(3-e)\bigr)=e.$$

Now compute the bracket:

$$e(3-e)=3e-e^{2},$$

so

$$13-e(3-e)=13-(3e-e^{2})=13-3e+e^{2}=e^{2}-3e+13.$$

Hence we have

$$a\,(e^{2}-3e+13)=e.$$

Finally, solving for $$a$$ gives

$$a=\frac{e}{e^{2}-3e+13}.$$

This value matches Option D.

Hence, the correct answer is Option D.

We start from the given implicit relation

$$y^2 + \log_e(\cos^2 x) = y,\qquad x\in\left(-\dfrac{\pi}{2},\dfrac{\pi}{2}\right).$$

Re-arranging,

$$y^2 - y + \log_e(\cos^2 x)=0.$$

First we determine the value of $$y$$ at $$x=0$$. Putting $$x=0$$ gives $$\cos 0 =1$$ and hence $$\log_e(\cos^2 0)=\log_e 1 =0$$. The equation reduces to

$$y^2 - y =0 \;\Longrightarrow\; y(y-1)=0,$$

so $$y(0)=0$$ or $$y(0)=1$$. Both roots are admissible; we shall keep the symbol $$y(0)$$ for the moment and let the computation decide the sign of the second derivative later, because the final result involves an absolute value.

To obtain derivatives we differentiate the implicit equation. Throughout, we treat $$y$$ as a function of $$x$$ and write $$y'=dy/dx,\; y''=d^2y/dx^2$$.

First derivative - We differentiate

$$y^2 - y + \log_e(\cos^2 x)=0$$

term by term. By the chain rule, $$d(y^2)/dx = 2yy'$$ and $$d(-y)/dx=-y'$$. For the logarithmic term we first recall the formula $$\dfrac{d}{dx}\bigl(\log_e u\bigr)=\dfrac{u'}{u}$$. Taking $$u=\cos^2 x$$ we have $$u'=2\cos x(-\sin x)=-\sin(2x)$$ and $$u=\cos^2 x$$, whence

$$\dfrac{d}{dx}\log_e(\cos^2 x)=\frac{-\sin(2x)}{\cos^2 x} =-\,\frac{2\sin x\cos x}{\cos^2 x}=-2\tan x.$$

Putting these pieces together, the differentiated equation is

$$2yy' - y' - 2\tan x = 0.$$

Collecting the $$y'$$ terms gives

$$(2y-1)y' = 2\tan x,$$

and so

$$y'=\frac{2\tan x}{\,2y-1\,}.$$

At $$x=0$$ we have $$\tan 0 =0$$, while $$2y(0)-1$$ is either $$-1$$ (if $$y(0)=0$$) or $$+1$$ (if $$y(0)=1$$). In either case the numerator is zero, hence

$$y'(0)=0.$$

Second derivative - We now differentiate the relation

$$(2y-1)y' = 2\tan x$$

once more with respect to $$x$$.

Using the product rule,

$$\frac{d}{dx}\bigl[(2y-1)y'\bigr]=(2y-1)y'' + 2y'(y'),$$

because $$d(2y-1)/dx = 2y'$$. On the right, $$d(2\tan x)/dx=2\sec^2 x$$. Therefore,

$$(2y-1)y'' + 2(y')^2 = 2\sec^2 x.$$

We now evaluate at $$x=0$$. We already established $$y'(0)=0$$, while $$\sec 0 =1$$. Hence the term containing $$(y')^2$$ vanishes and we obtain

$$(2y(0)-1)\,y''(0)=2\cdot 1^2=2,$$

so that

$$y''(0)=\frac{2}{\,2y(0)-1\,}.$$

If $$y(0)=1$$ the denominator is $$+1$$ and $$y''(0)=+2$$; if $$y(0)=0$$ the denominator is $$-1$$ and $$y''(0)=-2$$. In either situation the absolute value is the same:

$$|y''(0)| = 2.$$

We have also found $$y'(0)=0$$, so $$|y'(0)|+|y''(0)| = 0+2 = 2,$$ demonstrating that the other numerical options do not match.

Therefore the statement which is always true is $$|y''(0)| = 2$$.

Hence, the correct answer is Option C.

We have a function defined in two pieces,

$$ f(x)= \begin{cases} \dfrac{\pi}{4}+\tan^{-1}x, & |x|\le 1 \\[6pt] \dfrac12\,(|x|-1), & |x|>1 \end{cases} $$

Because the definition changes only at the points where the condition $$|x|=1$$ holds, that is, at $$x=-1$$ and $$x=1$$, any question about continuity or differentiability can arise only at these two points; elsewhere each individual formula is a standard elementary function and is automatically continuous and differentiable.

Continuity at $$x=1$$

The value of the function at $$x=1$$ comes from the first formula (since $$|1|\le1$$):

$$ f(1)=\frac{\pi}{4}+\tan^{-1}1 =\frac{\pi}{4}+\frac{\pi}{4} =\frac{\pi}{2}. $$

The right-hand limit, with $$x\to1^+$$, uses the second formula. For $$x>1$$ we have $$|x|=x$$, so

$$ \lim_{x\to1^+}f(x) =\lim_{x\to1^+}\frac12\,(x-1) =\frac12\,(1-1) =0. $$

The two numbers $$\dfrac{\pi}{2}$$ and $$0$$ are unequal, hence the right-hand limit is not equal to the value of the function. Therefore $$f$$ is not continuous at $$x=1$$.

Continuity at $$x=-1$$

Its value, now from the same first formula, is

$$ f(-1)=\frac{\pi}{4}+\tan^{-1}(-1) =\frac{\pi}{4}-\frac{\pi}{4} =0. $$

For $$x<-1$$ we have $$|x|=-x$$, so using the second formula the left-hand limit becomes

$$ \lim_{x\to-1^-}f(x) =\lim_{x\to-1^-}\frac12\,((-x)-1) =\frac12\,\bigl(-(-1)-1\bigr) =\frac12\,(1-1) =0. $$

The right-hand limit (from the first formula) is the same number, $$0$$, so both one-sided limits exist and equal the value of the function. Hence $$f$$ is continuous at $$x=-1$$.

Because the only discontinuity occurs at $$x=1$$, we conclude that

$$ f(x)\text{ is continuous on }\mathbb R-\{1\}. $$

Differentiability at $$x=-1$$

The derivative inside $$|x|\le1$$ is obtained from the standard rule $$\dfrac{d}{dx}\tan^{-1}x=\dfrac1{1+x^2}$$. Thus, for $$-1<x<1$$,

$$ f'(x)=\frac{1}{1+x^2}. $$

Taking the right-hand derivative at $$x=-1$$, we substitute $$x=-1$$:

$$ f'_+( -1)=\frac1{1+(-1)^2}=\frac12. $$

For $$x<-1$$ the expression $$f(x)=\dfrac12(-x-1)$$ can be differentiated directly, giving

$$ f'(x)=\frac12(-1)=-\frac12. $$

This is a constant, so the left-hand derivative at $$x=-1$$ is

$$ f'_-( -1)=-\frac12. $$

Since $$\dfrac12\neq-\dfrac12$$, the two one-sided derivatives disagree and $$f$$ is not differentiable at $$x=-1$$.

Differentiability at $$x=1$$

Differentiability always implies continuity, but we have already shown that $$f$$ is not even continuous at $$x=1$$. Therefore $$f$$ is certainly not differentiable at $$x=1$$.

Conclusion

We have shown:

• Continuous everywhere except at $$x=1$$.
• Differentiable everywhere except at $$x=-1$$ and $$x=1$$.

So the function is continuous on $$\mathbb R-\{1\}$$ and differentiable on $$\mathbb R-\{-1,1\}$$.

Hence, the correct answer is Option A.

For the given piece-wise definition we have

$$f(x)=\begin{cases} k_1\,(x-\pi)^2-1,& x\le \pi\\[4pt] k_2\cos x,& x>\pi \end{cases}$$

To be twice differentiable at the joining point $$x=\pi$$, the function itself, its first derivative and its second derivative must all be continuous there.

1. Continuity of the function at $$x=\pi$$

Left-hand value:

$$f(\pi^-)=k_1\,(\pi-\pi)^2-1=k_1\cdot 0-1=-1$$

Right-hand value:

$$f(\pi^+)=k_2\cos\pi=k_2(-1)=-k_2$$

For continuity we equate the two:

$$-1=-k_2\Longrightarrow k_2=1$$

2. Continuity of the first derivative at $$x=\pi$$

First we write the standard differentiation formulas we will use:

• For $$x^n$$ we use $$\dfrac{d}{dx}\bigl(x^n\bigr)=n\,x^{\,n-1}.$$

• For $$\cos x$$ we use $$\dfrac{d}{dx}\bigl(\cos x\bigr)=-\sin x.$$

Left-hand derivative:

$$f'(x)=\dfrac{d}{dx}\bigl(k_1(x-\pi)^2-1\bigr)=k_1\cdot 2(x-\pi)=2k_1(x-\pi)$$

Therefore

$$f'(\pi^-)=2k_1(\pi-\pi)=0$$

Right-hand derivative (using $$k_2=1$$ already obtained):

$$f'(x)=\dfrac{d}{dx}\bigl(k_2\cos x\bigr)=-k_2\sin x=-\sin x$$

Hence

$$f'(\pi^+)=-(\sin\pi)=0$$

Because both one-sided derivatives equal $$0$$, the first derivative is continuous automatically for every $$k_1$$ when $$k_2=1$$. So we proceed to the second derivative.

3. Continuity of the second derivative at $$x=\pi$$

The second derivative on the left side is obtained by differentiating $$f'(x)=2k_1(x-\pi)$$ once more:

$$f''(x)=\dfrac{d}{dx}\bigl(2k_1(x-\pi)\bigr)=2k_1$$

Thus

$$f''(\pi^-)=2k_1$$

On the right side we differentiate $$f'(x)=-\sin x$$ again, recalling the formula $$\dfrac{d}{dx}(\sin x)=\cos x$$ and carrying the minus sign:

$$f''(x)=\dfrac{d}{dx}\bigl(-\sin x\bigr)=-\cos x$$

So

$$f''(\pi^+)=-(\cos\pi)= -(-1)=1$$

For the second derivative to be continuous we need

$$f''(\pi^-)=f''(\pi^+) \Longrightarrow 2k_1=1$$

Solving this simple linear equation gives

$$k_1=\dfrac{1}{2}$$

Combining the two conditions, we finally obtain

$$\bigl(k_1,k_2\bigr)=\left(\dfrac12,\,1\right)$$

Hence, the correct answer is Option A.

We are given the piece-wise real function

$$ f(x)= \begin{cases} x^{5}\sin\!\left(\dfrac1x\right)+5x^{2}, & x<0,\\[6pt] 0, & x=0,\\[6pt] x^{5}\cos\!\left(\dfrac1x\right)+\lambda x^{2}, & x>0. \end{cases} $$

Our task is to find the value of the constant $$\lambda$$ for which the second derivative $$f''(0)$$ exists.

According to the definition of a derivative, the first derivative at zero is

$$ f'(0)=\lim_{x\to0}\frac{f(x)-f(0)}{x}. $$

We therefore begin by computing $$f'(0)$$ from the left and from the right.

Left side ($$x<0$$)

For $$x<0$$ we have $$f(x)=x^{5}\sin\!\left(\dfrac1x\right)+5x^{2}$$, so

$$ \frac{f(x)-f(0)}{x} =\frac{x^{5}\sin\!\left(\dfrac1x\right)+5x^{2}-0}{x} =x^{4}\sin\!\left(\dfrac1x\right)+5x. $$

Because $$-1\le\sin\theta\le1$$ for every real $$\theta$$, the factor $$x^{4}$$ forces the first term to $$0$$ as $$x\to0$$, and the second term $$5x$$ also tends to $$0$$. Hence

$$ \lim_{x\to0^-}\frac{f(x)-f(0)}{x}=0. $$

Right side ($$x>0$$)

For $$x>0$$ we have $$f(x)=x^{5}\cos\!\left(\dfrac1x\right)+\lambda x^{2}$$, so

$$ \frac{f(x)-f(0)}{x} =\frac{x^{5}\cos\!\left(\dfrac1x\right)+\lambda x^{2}-0}{x} =x^{4}\cos\!\left(\dfrac1x\right)+\lambda x. $$

Again, the boundedness of $$\cos$$ and the explicit factor of $$x$$ make both terms approach $$0$$ as $$x\to0$$. Thus

$$ \lim_{x\to0^+}\frac{f(x)-f(0)}{x}=0. $$

Since both one-sided limits are equal, we have

$$ f'(0)=0. $$

Next we recall the definition of the second derivative:

$$ f''(0)=\lim_{x\to0}\frac{f'(x)-f'(0)}{x}. $$

Therefore we now compute the first derivative away from zero and then take the above limit.

Derivative for $$x<0$$

Write $$g(x)=x^{5}\sin\!\left(\tfrac1x\right).$$ Using the product rule and the chain rule,

$$ \frac{d}{dx}\,x^{5}\sin\!\left(\tfrac1x\right) =5x^{4}\sin\!\left(\tfrac1x\right) +x^{5}\cos\!\left(\tfrac1x\right)\left(-\frac1{x^{2}}\right) =5x^{4}\sin\!\left(\tfrac1x\right)-x^{3}\cos\!\left(\tfrac1x\right). $$

The derivative of $$5x^{2}$$ is plainly $$10x$$. Hence for $$x<0$$

$$ f'(x)=5x^{4}\sin\!\left(\tfrac1x\right)-x^{3}\cos\!\left(\tfrac1x\right)+10x. $$

Derivative for $$x>0$$

For $$x^{5}\cos\!\left(\tfrac1x\right)$$, again apply the product and chain rules:

$$ \frac{d}{dx}\,x^{5}\cos\!\left(\tfrac1x\right) =5x^{4}\cos\!\left(\tfrac1x\right) +x^{5}\!\left(-\sin\!\left(\tfrac1x\right)\right)\!\left(-\frac1{x^{2}}\right) =5x^{4}\cos\!\left(\tfrac1x\right)+x^{3}\sin\!\left(\tfrac1x\right). $$

The derivative of $$\lambda x^{2}$$ is $$2\lambda x$$. Consequently, for $$x>0$$

$$ f'(x)=5x^{4}\cos\!\left(\tfrac1x\right)+x^{3}\sin\!\left(\tfrac1x\right)+2\lambda x. $$

We now evaluate the limit that defines $$f''(0)$$ separately from the left and from the right.

Left-hand limit

For $$x<0$$, subtract $$f'(0)=0$$ and divide by $$x$$:

$$ \frac{f'(x)-f'(0)}{x} =\frac{5x^{4}\sin\!\left(\tfrac1x\right)-x^{3}\cos\!\left(\tfrac1x\right)+10x}{x} =5x^{3}\sin\!\left(\tfrac1x\right)-x^{2}\cos\!\left(\tfrac1x\right)+10. $$

The first two terms contain factors $$x^{3}$$ and $$x^{2}$$, respectively, both of which drive them to $$0$$ because $$\sin$$ and $$\cos$$ stay between $$-1$$ and $$1$$. Therefore

$$ \lim_{x\to0^-}\frac{f'(x)-f'(0)}{x}=10. $$

Right-hand limit

For $$x>0$$ we get

$$ \frac{f'(x)-f'(0)}{x} =\frac{5x^{4}\cos\!\left(\tfrac1x\right)+x^{3}\sin\!\left(\tfrac1x\right)+2\lambda x}{x} =5x^{3}\cos\!\left(\tfrac1x\right)+x^{2}\sin\!\left(\tfrac1x\right)+2\lambda. $$

Again the first two terms shrink to $$0$$ as $$x\to0$$, leaving

$$ \lim_{x\to0^+}\frac{f'(x)-f'(0)}{x}=2\lambda. $$

For the second derivative $$f''(0)$$ to exist, the left-hand and right-hand limits must coincide; hence we require

$$ 10 = 2\lambda. $$

Solving immediately yields

$$ \lambda = 5. $$

So, the answer is $$5$$.

We have a piece-wise definition of the function $$f$$ on the open interval $$\left(-\tfrac13,\; \tfrac13\right)$$:

$$ f(x)= \begin{cases} \dfrac{1}{x}\,\log_e\!\left(\dfrac{1+3x}{\,1-2x\,}\right), & \text{when } x\neq 0,\\[6pt] k, & \text{when } x=0. \end{cases} $$

The problem asks for the real number $$k$$ that makes the function continuous at $$x=0$$. By the definition of continuity, we need

$$ \lim_{x\to 0} f(x)=f(0)=k. $$

Thus we must evaluate the limit of the first branch as $$x\to 0$$ and then set that equal to $$k$$.

Observe that as $$x\to 0$$, both the numerator and the denominator inside the first branch approach zero:

$$ \log_e\!\left(\dfrac{1+3x}{1-2x}\right)\;\xrightarrow{x\to 0}\;\log_e 1 = 0, \quad x\xrightarrow{x\to 0}0, $$

so the limit has the indeterminate form $$\dfrac 0 0$$. The standard way to handle this form is to quote and use L’Hôpital’s Rule, which states:

“If $$\displaystyle\lim_{x\to a}\!g(x)=0$$ and $$\displaystyle\lim_{x\to a}\!h(x)=0$$ (or both infinite) and the derivatives exist near $$a$$, then

$$ \lim_{x\to a}\dfrac{g(x)}{h(x)}=\lim_{x\to a}\dfrac{g'(x)}{h'(x)}, $$

provided the right-hand limit exists.”

Here we identify

$$ g(x)=\log_e\!\left(\dfrac{1+3x}{1-2x}\right),\qquad h(x)=x. $$

We first find the derivative of $$g(x)$$. To simplify the logarithm we separate it using the logarithm identity $$\log(a/b)=\log a-\log b$$:

$$ g(x)=\log_e(1+3x)\;-\;\log_e(1-2x). $$

Now differentiate term by term:

$$ g'(x)=\dfrac{d}{dx}\bigl[\log_e(1+3x)\bigr]-\dfrac{d}{dx}\bigl[\log_e(1-2x)\bigr]. $$

Using the basic derivative formula $$\dfrac{d}{dx}\log_e(1+ax)=\dfrac{a}{1+ax}$$, we obtain

$$ g'(x)=\dfrac{3}{1+3x}-\!\Bigl(-\dfrac{2}{1-2x}\Bigr) =\dfrac{3}{1+3x}+\dfrac{2}{1-2x}. $$

The derivative of the denominator $$h(x)=x$$ is simply

$$ h'(x)=\dfrac{d}{dx}(x)=1. $$

Applying L’Hôpital’s Rule, the desired limit becomes

$$ \lim_{x\to 0}\dfrac{g(x)}{h(x)} =\lim_{x\to 0}\dfrac{g'(x)}{h'(x)} =\lim_{x\to 0}\Bigl[\dfrac{3}{1+3x}+\dfrac{2}{1-2x}\Bigr]. $$

Now we simply substitute $$x=0$$ into the rational expressions because they are continuous there:

$$ \dfrac{3}{1+3(0)}+\dfrac{2}{1-2(0)} =\dfrac{3}{1}+\dfrac{2}{1} =3+2 =5. $$

Thus

$$ \lim_{x\to 0} \dfrac{1}{x}\log_e\!\left(\dfrac{1+3x}{\,1-2x\,}\right)=5. $$

For continuity at the origin we therefore require

$$ k = 5. $$

Hence, the correct answer is Option 5.

We are given the function

$$f(x)=x\,[\,\frac{x}{2}\,],\qquad -10<x<10,$$

where $$[t]$$ denotes the greatest-integer (floor) function. Our task is to count the points inside the open interval $$(-10,10)$$ where $$f(x)$$ is not continuous.

First recall a basic fact about the greatest-integer function:

Whenever the argument of $$[\,\cdot\,]$$ crosses an integer, the value of the greatest-integer function jumps by $$1$$. In symbols, $$[t]$$ is discontinuous exactly at all integer values of $$t$$.

In our expression the argument of the floor function is $$\dfrac{x}{2}$$, so the jump (and therefore the possible discontinuity) occurs whenever

$$\frac{x}{2}=k\quad\text{with }k\in\mathbb Z.$$

Solving for $$x$$ we obtain

$$x=2k,\quad k\in\mathbb Z.$$

Thus the only potential points of discontinuity for $$f(x)$$ in the interval $$(-10,10)$$ are the even integers lying strictly between $$-10$$ and $$10$$:

$$x=-8,-6,-4,-2,0,2,4,6,8.$$

There are nine such points. We must, however, check each of them because the product by the factor $$x$$ might cancel the jump at some specific point.

Let us analyse each candidate point.

1. The point $$x=0$$.

For $$x>0$$ and sufficiently close to $$0$$ we have $$0<x<2$$, so $$\dfrac{x}{2}\in(0,1)$$ and hence $$\bigl[\dfrac{x}{2}\bigr]=0$$. Therefore

$$f(x)=x\cdot 0=0 \quad\text{for }0<x<2.$$

For $$x<0$$ and sufficiently close to $$0$$ we have $$-2<x<0$$, so $$\dfrac{x}{2}\in(-1,0)$$ and hence $$\bigl[\dfrac{x}{2}\bigr]=-1$$. Therefore

$$f(x)=x\cdot(-1)=-x \quad\text{for }-2<x<0.$$

Taking the limit from the right:

$$\lim_{x\to0^{+}}f(x)=\lim_{x\to0^{+}}0=0.$$

Taking the limit from the left:

$$\lim_{x\to0^{-}}f(x)=\lim_{x\to0^{-}}(-x)=0.$$

Both one-sided limits are equal and equal to zero. The actual value of the function at $$x=0$$ is

$$f(0)=0\cdot\Bigl[\frac{0}{2}\Bigr]=0\cdot0=0.$$

Hence the function is continuous at $$x=0$$. Therefore $$x=0$$ does not contribute to the count of discontinuities.

2. The other even integers: $$x=\pm2,\pm4,\pm6,\pm8$$.

We illustrate the reasoning for a representative point, say $$x=2k$$ with $$k\neq0$$, because the algebra is identical for every such $$k$$.

Pick $$x_{0}=2k$$ with $$k\neq0$$. Then $$\dfrac{x_{0}}{2}=k$$ is an integer. Setting $$x=x_{0}+h$$ with a tiny positive $$h$$ (approach from the right) we have

$$\frac{x}{2}=k+\frac{h}{2},\qquad 0<h\ll1,$$

so

$$\Bigl[\frac{x}{2}\Bigr]=k \quad\text{for }x\to x_{0}^{+}.$$

Therefore the right-hand limit is

$$\lim_{x\to x_{0}^{+}}f(x)=\lim_{h\to0^{+}}(x_{0}+h)\,k \;=\;x_{0}\,k.$$

Now approach from the left, i.e. take $$x=x_{0}-h$$ with $$0<h\ll1$$:

$$\frac{x}{2}=k-\frac{h}{2}\quad\Longrightarrow\quad \Bigl[\frac{x}{2}\Bigr]=k-1.$$

Thus the left-hand limit is

$$\lim_{x\to x_{0}^{-}}f(x)=\lim_{h\to0^{+}}(x_{0}-h)\,(k-1) \;=\;x_{0}\,(k-1).$$

Compute the difference between the two one-sided limits:

$$x_{0}\,k - x_{0}\,(k-1)=x_{0}.$$

Since $$x_{0}=2k\neq0$$, this difference is non-zero. Therefore the two one-sided limits are different, which means the function is discontinuous at $$x_{0}=2k.$$

The same calculation applies verbatim for every non-zero even integer in our list. Consequently $$f(x)$$ is discontinuous at each of

$$x=-8,-6,-4,-2,2,4,6,8.$$

Counting the discontinuities

We found discontinuities at eight points and confirmed continuity at $$x=0$$. No other points inside $$(-10,10)$$ cause trouble, so the total number of discontinuities of $$f(x)$$ in the given interval is

$$8.$$

So, the answer is $$8$$.

We are given the function $$f(x)=\left|\,2-\bigl|x-3\bigr|\,\right|$$ for all real numbers $$x$$. A point where a function contains the symbol $$|\,\cdot\,|$$ can fail to be differentiable in only one of two situations:

1. The outer absolute value changes from the form $$|u|=u$$ to $$|u|=-u$$, that is, when its argument $$u$$ becomes $$0$$.
2. The inner expression itself is an absolute-value function such as $$|x-3|$$, which is not differentiable at the point where its own argument is zero.

We therefore inspect the two absolute values present.

(i) Zero of the inner absolute value.
The inner symbol is $$|x-3|$$, which becomes zero when $$x-3=0$$, i.e. at $$x=3$$. Because $$|x-3|$$ is not differentiable at that point, the composite function $$f(x)$$ can also fail to be differentiable at $$x=3$$.

(ii) Zero of the outer absolute value.
The argument of the outer absolute value is $$2-|x-3|$$. Setting it equal to zero, we get $$2-|x-3|=0\;\Longrightarrow\;|x-3|=2 \;\Longrightarrow\;x-3=\pm2 \;\Longrightarrow\;x=1\;\text{ or }\;x=5.$$ Thus $$x=1$$ and $$x=5$$ are two more candidate points of non-differentiability.

No other values of $$x$$ make either absolute value switch slope, so the set of points where $$f(x)$$ is not differentiable is $$S=\{1,\,3,\,5\}.$$

We now need the sum $$\sum_{x\in S} f\!\bigl(f(x)\bigr) =f\!\bigl(f(1)\bigr)+f\!\bigl(f(3)\bigr)+f\!\bigl(f(5)\bigr).$$ To compute these terms smoothly, we first write $$f(x)$$ without nested absolute values. Let us consider the value of $$|x-3|$$ and then of $$f(x)=|2-|x-3||$$ step by step.

When $$|x-3|\le 2$$ (that is, $$1\le x\le 5$$) the inner quantity $$2-|x-3|$$ is non-negative, so the outer absolute value does nothing and $$f(x)=2-|x-3|.$$ When $$|x-3|>2$$ (that is, $$x<1$$ or $$x>5$$) the inner quantity is negative, so the outer absolute value adds a minus sign and $$f(x)=|x-3|-2.$$ Next we remove the remaining absolute value $$|x-3|$$ to obtain four linear pieces:

For $$1\le x\le 3$$: here $$|x-3|=3-x,$$ so $$f(x)=2-(3-x)=x-1.$$ For $$3\le x\le 5$$: here $$|x-3|=x-3,$$ so $$f(x)=2-(x-3)=5-x.$$ For $$x>5$$: here $$|x-3|=x-3,$$ so $$f(x)=x-3-2=x-5.$$ For $$x<1$$: here $$|x-3|=3-x,$$ so $$f(x)=3-x-2=1-x.$$

Using these explicit formulas we evaluate $$f(x)$$ at the three points in $$S$$.

At $$x=1$$ (lies in the interval $$1\le x\le 3$$):
$$f(1)=1-1=0.$$ At $$x=3$$ (lies in either $$1\le x\le 3$$ or $$3\le x\le 5$$, both give the same value):
$$f(3)=3-1=2 \quad\text{or}\quad f(3)=5-3=2.$$ At $$x=5$$ (lies in $$3\le x\le 5$$):
$$f(5)=5-5=0.$$

Now we must feed these results back into the function once more.

For $$x=1$$ we need $$f\!\bigl(f(1)\bigr)=f(0).$$
Since $$0<1,$$ the appropriate formula is $$f(x)=1-x,$$ giving $$f(0)=1-0=1.$$ For $$x=3$$ we need $$f\!\bigl(f(3)\bigr)=f(2).$$
Because $$2\in[1,3],$$ we again use $$f(x)=x-1,$$ so $$f(2)=2-1=1.$$ For $$x=5$$ we need $$f\!\bigl(f(5)\bigr)=f(0),$$ already evaluated above as $$1.$$

Adding the three results, we obtain $$\sum_{x\in S} f\!\bigl(f(x)\bigr)=1+1+1=3.$$ So, the answer is $$3$$.

We have the first‐level function defined as $$f(x)=15-|x-10|,\;x\in\mathbb R.$$

To discuss the differentiability of the composite $$g(x)=f\!\bigl(f(x)\bigr),$$ we must recall a fact about compositions: a composition $$F(G(x))$$ fails to be differentiable at a point $$x=a$$ if (i) the inner function $$G(x)$$ is not differentiable at $$x=a$$, or (ii) the outer function $$F(u)$$ is not differentiable at the value $$u=G(a).$$ We shall therefore find:

1. The point(s) where $$f(x)$$ itself is not differentiable.
2. The point(s) where the argument of the outer $$f$$ inside $$g(x)$$ equals the non-differentiability point of $$f$$.

Step 1 : Differentiability of $$f(x)$$

The expression $$f(x)=15-|x-10|$$ contains an absolute value. We know the standard result:

For $$h(x)=|x-c|,$$ the function $$h(x)$$ is not differentiable at $$x=c.$$ Everywhere else its derivative exists.

Here $$|x-10|$$ has a corner at $$x=10,$$ so $$f(x)$$ is not differentiable only at

$$x=10.$$

Step 2 : Values of $$x$$ that make the argument of the outer $$f$$ equal to 10

Inside the composite we have $$f(x)$$ fed into another $$f$$. The outer $$f$$ will have a corner whenever its argument equals 10. Hence we must solve

$$f(x)=10.$$

Substituting the definition of $$f(x),$$ we get

$$15-|x-10|=10.$$

Transposing terms gives

$$|x-10| = 15-10 =5.$$

Using the property $$|y|=k \Longrightarrow y=\pm k,$$ we obtain

$$x-10 = 5 \quad\text{or}\quad x-10 = -5.$$

Thus

$$x = 15 \quad\text{or}\quad x = 5.$$

Step 3 : Collecting all points of non-differentiability for $$g(x)$$

As explained, $$g(x)=f(f(x))$$ fails to be differentiable at

• $$x=10$$ (inner $$f$$ is not differentiable), and
• $$x=5,\;15$$ (outer $$f$$ is hit precisely at its corner because $$f(x)=10$$ there).

No other values of $$x$$ cause either type of failure, so the complete set is

$$\{5,\;10,\;15\}.$$

Hence, the correct answer is Option A.

We have a real-valued function defined on the open interval $$\left(\dfrac{\pi}{6},\dfrac{\pi}{3}\right)$$ by

$$ f(x)= \begin{cases} \dfrac{\sqrt{2}\cos x-1}{\cot x-1}, & x\neq\dfrac{\pi}{4}\\[4pt] k, & x=\dfrac{\pi}{4} \end{cases} $$

For continuity at the point $$x=\dfrac{\pi}{4}$$ we require the limit of the first expression as $$x\to\dfrac{\pi}{4}$$ to exist and to be equal to $$k$$, that is

$$ k=\lim_{x\to\pi/4}\dfrac{\sqrt{2}\cos x-1}{\cot x-1}. $$

We now evaluate this limit step by step. First we rewrite the denominator in terms of sine and cosine only. Remember the definition $$\cot x=\dfrac{\cos x}{\sin x}$$. Substituting this, we obtain

$$ \cot x-1=\dfrac{\cos x}{\sin x}-1=\dfrac{\cos x-\sin x}{\sin x}. $$

Putting this back into the fraction gives

$$ f(x)=\dfrac{\sqrt{2}\cos x-1}{\dfrac{\cos x-\sin x}{\sin x}} =\dfrac{\bigl(\sqrt{2}\cos x-1\bigr)\sin x}{\cos x-\sin x}. $$

So the required limit becomes

$$ \lim_{x\to\pi/4}\dfrac{\bigl(\sqrt{2}\cos x-1\bigr)\sin x}{\cos x-\sin x}. $$

Notice that at $$x=\dfrac{\pi}{4}$$ both the numerator and the denominator separately go to zero, because

$$ \sqrt{2}\cos\!\left(\dfrac{\pi}{4}\right)-1=\sqrt{2}\cdot\dfrac{\sqrt{2}}{2}-1=1-1=0 $$

and

$$ \cos\!\left(\dfrac{\pi}{4}\right)-\sin\!\left(\dfrac{\pi}{4}\right)=\dfrac{\sqrt{2}}{2}-\dfrac{\sqrt{2}}{2}=0. $$

Hence the fraction is of the indeterminate type $$\dfrac{0}{0}$$, so we apply the L’Hospital rule. The rule states that if the limits of numerator and denominator give $$0/0$$, then

$$ \lim_{x\to a}\dfrac{u(x)}{v(x)} =\lim_{x\to a}\dfrac{u'(x)}{v'(x)}, $$

provided that the latter limit exists. We therefore differentiate the numerator and the denominator separately.

Let

$$ U(x)=\bigl(\sqrt{2}\cos x-1\bigr)\sin x,\qquad V(x)=\cos x-\sin x. $$

Differentiating $$U(x)$$ with respect to $$x$$, we use the product rule $$\dfrac{d}{dx}\bigl[p(x)q(x)\bigr]=p'(x)q(x)+p(x)q'(x)$$. Writing $$p(x)=\sqrt{2}\cos x-1$$ and $$q(x)=\sin x$$, we get

$$ U'(x)=\bigl[-\sqrt{2}\sin x\bigr]\sin x+\bigl(\sqrt{2}\cos x-1\bigr)\cos x =-\sqrt{2}\sin^{2}x+\bigl(\sqrt{2}\cos x-1\bigr)\cos x. $$

Next we differentiate $$V(x)$$. Using $$\dfrac{d}{dx}\cos x=-\sin x$$ and $$\dfrac{d}{dx}\sin x=\cos x$$, we have

$$ V'(x)=-\sin x-\cos x. $$

Now we evaluate these derivatives at $$x=\dfrac{\pi}{4}$$. Recall that

$$ \sin\!\left(\dfrac{\pi}{4}\right)=\cos\!\left(\dfrac{\pi}{4}\right)=\dfrac{\sqrt{2}}{2}. $$

Therefore, for the numerator derivative:

$$ U'\!\left(\dfrac{\pi}{4}\right)= -\sqrt{2}\left(\dfrac{\sqrt{2}}{2}\right)^2 +\Bigl(\sqrt{2}\cdot\dfrac{\sqrt{2}}{2}-1\Bigr)\dfrac{\sqrt{2}}{2} =-\sqrt{2}\cdot\dfrac12+\bigl(1-1\bigr)\dfrac{\sqrt{2}}{2} =-\dfrac{\sqrt{2}}{2}. $$

(The second term vanishes because $$\sqrt{2}\cdot\dfrac{\sqrt{2}}{2}-1=1-1=0$$.)

For the denominator derivative:

$$ V'\!\left(\dfrac{\pi}{4}\right)= -\dfrac{\sqrt{2}}{2}-\dfrac{\sqrt{2}}{2} =-\sqrt{2}. $$

Hence, by L’Hospital rule, the required limit is

$$ \lim_{x\to\pi/4}\dfrac{U(x)}{V(x)} =\dfrac{U'\!\left(\dfrac{\pi}{4}\right)}{V'\!\left(\dfrac{\pi}{4}\right)} =\dfrac{-\dfrac{\sqrt{2}}{2}}{-\sqrt{2}} =\dfrac{1}{2}. $$

Thus we must choose

$$ k=\dfrac12. $$

Hence, the correct answer is Option A.