Q. If $y = \tan^{- 1}{\frac{\sqrt{1 + x^{2}} - \sqrt{1 - x^{2}}}{\sqrt{1 + x^{2}} + \sqrt{1 - x^{2}}},\ \ \ then\frac{dy}{dx}\ }is\ equal\ to$

A) $\frac{x^{2}}{\sqrt{1 - x^{4}}}$
B) $\frac{x^{2}}{\sqrt{1 + x^{4}}}$
C) $\frac{x}{\sqrt{1 + x^{4}}}$
D) $\frac{x}{\sqrt{1 - x^{4}}}$
Explanation

(d)
Put $x^{2} = \cos{2\theta\ }$in the given equation, we get
$y = \tan^{- 1}\frac{\sqrt{1 + \cos{2\theta}} - \sqrt{1 - \cos{2\theta}}}{\sqrt{1 + \cos{2\theta}} + \sqrt{1 - \cos{2\theta}}}$
$= \tan^{- 1}\frac{\cos{\theta - sin\theta}}{\cos{\theta + \sin\theta}}$
$= \tan^{- 1}{\tan\left( \frac{\pi}{4} - \theta \right)}$
$\Rightarrow \ y = \frac{\pi}{4} - \theta = \frac{\pi}{4} - \frac{1}{2}\cos^{- 1}x^{2}$
$\Rightarrow \ \frac{dy}{dx} = 0 - \frac{1}{2}\left( - \frac{(2x)}{\sqrt{1 - x^{4}}} \right) = \frac{x}{\sqrt{1 - x^{4}}}$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

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