Question:
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:
Correct Option: 1
Solution:
$\because \quad$ Curve is given as :
$y=x^{2}-1$
$\Rightarrow \quad \frac{d y}{d x}=2 x$
$\Rightarrow \quad\left(\frac{d y}{d x}\right)_{(2,3)}=4$
equation of tangent at $(2,3)$
$(y-3)=4(x-2)$
$\Rightarrow y=4 x-5$
but $x=0$
$\Rightarrow y=-5$
Here the curve cuts $\mathrm{Y}$-axis
$\therefore$ required area
$=\frac{1}{4} \int_{-5}^{3}(y+5) d y-\int_{-1}^{3} \sqrt{y+1} d y$
$=\frac{1}{4}\left[\frac{y^{2}}{2}+5 y\right]_{-5}^{3} \frac{-2}{3}\left[(y+1)^{3 / 2}\right]_{-1}^{3}$
$=\frac{1}{4}\left[\frac{9}{2}+15-\frac{25}{2}+25\right]-\frac{2}{3}\left[4^{3 / 2}-0\right]$
$=\frac{32}{4}-\frac{16}{3}=\frac{8}{3}$ sq-units.