If $\theta$ denotes the acute angle between the curves $y=10-x^2$ and $y=2+x^2$, at a point of the…

If $\theta$ denotes the acute angle between the curves $y=10-x^2$ and $y=2+x^2$, at a point of the intersection, then $|\tan \theta|$ is equal to
  1. $\frac{8}{15}$
  2. $\frac{8}{17}$
  3. $\frac{4}{9}$
  4. $\frac{7}{17}$

Solution

$\begin{aligned} & y=10-x^2 ...(i)\\ & y=2+x^2...(ii) \end{aligned}$
Solving (i) and (ii), we get $y=6$ From (i), $6=10-x^2 \Rightarrow x= \pm 2$ Differentiating (i) w.r.t. $x$, we get $\frac{\mathrm{d} y}{\mathrm{~d} x}=-2 x \Rightarrow\left(\frac{\mathrm{~d} y}{\mathrm{~d} x}\right)_{(-2,6)}=4$
Differentiating (ii) w.r.t. $x$, we get $\begin{aligned} & \frac{\mathrm{d} y}{\mathrm{~d} x}=2 x \Rightarrow\left(\frac{\mathrm{~d} y}{\mathrm{~d} x}\right)_{(-2,6)}=-4 \\ \therefore \quad & \tan \theta=\left|\frac{4-(-4)}{1+4(-4)}\right|=\left|\frac{8}{-15}\right| \Rightarrow|\tan \theta|=\frac{8}{15} \end{aligned}$

Asked in: MHT CET 2024 (16 May Shift 1)

Practice more Applications of Derivatives questions on Aicharya