Q. If $\theta$ is the angle between the curves $x\ y = 2$ and $x^{2} + 4y = 0$ , then $\tan\theta$ is equal to

A) 1
B) -1
C) 2
D) 3
Explanation

(d)
The point of intersection of given curve is $( - 2,\ - 1)$
On differentiating the given curve respectively, we get
$x\frac{dy}{dx} + y = 0\ \ \Rightarrow \ \ \frac{dy}{dx} = - \frac{y}{x}$
$\Rightarrow \ \ \ \ \ m_{1} = \left( \frac{dy}{dx} \right)_{( - 2,\ - 1)} = - \frac{1}{2}$
And $2x + 4\frac{dy}{dx} = 0$
$\Rightarrow \ \ \frac{dy}{dx} = - \frac{x}{2}$
$\Rightarrow \ \ \ \ m_{2} = \left( \frac{dy}{dx} \right)_{( - 2,\ - 1)} = 1$
$\therefore\ \ \ \ \tan\theta = \left| \frac{m_{1} - m_{2}}{1 + m_{1}m_{2}} \right| = \left| \frac{- \frac{1}{2} - 1}{1 - \frac{1}{2}} \right| = 3$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.