Sign in
Please select an account to continue using cracku.in
↓ →
Join Our JEE Preparation Group
Prep with like-minded aspirants; Get access to free daily tests and study material.
The area (in sq. units) bounded by the parabola $$y = x^2 - 1$$, the tangent at the point (2, 3) to it and the $$y$$-axis is:
We have the parabola whose equation is $$y = x^{2}-1$$. To write the equation of the tangent at the point $$(2,3)$$ on this parabola, we first need the slope of the tangent.
For a curve $$y = f(x)$$, the slope of the tangent at any point is given by the derivative $$\dfrac{dy}{dx}$$. Here
$$\dfrac{dy}{dx} = \dfrac{d}{dx}(x^{2}-1) = 2x.$$
At the point $$(2,3)$$ we substitute $$x = 2$$ to get
$$m = 2(2) = 4.$$
The point-slope form of a tangent is $$y - y_{1} = m(x - x_{1})$$. Substituting $$(x_{1},y_{1}) = (2,3)$$ and $$m = 4$$, we obtain
$$y - 3 = 4\,(x - 2).$$
Expanding,
$$y - 3 = 4x - 8$$
$$y = 4x - 5.$$
Thus, the tangent line is $$y = 4x - 5$$. Observe that it cuts the $$y$$-axis (where $$x = 0$$) at the point $$(0,-5)$$. The parabola meets the $$y$$-axis at $$(0,-1)$$. Hence the vertical line $$x = 0$$ together with the curves
$$y = x^{2}-1 \quad\text{and}\quad y = 4x - 5$$
encloses the required region. Between $$x = 0$$ and $$x = 2$$ (the $$x$$-coordinate of the point of tangency) the parabola lies above the tangent, because
$$\bigl(x^{2}-1\bigr) - (4x - 5) = x^{2} - 4x + 4 = (x - 2)^{2} \ge 0.$$
Therefore, the area $$A$$ is obtained by integrating the vertical difference “parabola minus tangent’’ from $$x = 0$$ to $$x = 2$$:
$$A = \int_{0}^{2} \Bigl[(x^{2}-1) - (4x - 5)\Bigr]\,dx = \int_{0}^{2} \bigl(x^{2} - 4x + 4\bigr)\,dx.$$
Now we integrate term-by-term:
$$\int x^{2}\,dx = \frac{x^{3}}{3}, \qquad \int (-4x)\,dx = -2x^{2}, \qquad \int 4\,dx = 4x.$$
Putting the limits $$0$$ to $$2$$, we get
$$A = \left[\frac{x^{3}}{3} - 2x^{2} + 4x\right]_{0}^{2} = \left(\frac{2^{3}}{3} - 2(2)^{2} + 4(2)\right) - \left(\frac{0^{3}}{3} - 2(0)^{2} + 4(0)\right).$$
Simplifying the expression at $$x = 2$$:
$$\frac{2^{3}}{3} = \frac{8}{3}, \quad -2(2)^{2} = -2 \times 4 = -8, \quad 4(2) = 8.$$
Adding these three values,
$$\frac{8}{3} - 8 + 8 = \frac{8}{3} + 0 = \frac{8}{3}.$$
The value at $$x = 0$$ is clearly $$0$$, so
$$A = \frac{8}{3}\ \text{square units}.$$
Hence, the correct answer is Option B.
Create a FREE account and get:
Predict your JEE Main percentile, rank & performance in seconds
Educational materials for JEE preparation
Ask our AI anything
AI can make mistakes. Please verify important information.
AI can make mistakes. Please verify important information.