Q. For $0 < x < 2,\frac{d}{dx}\ \left( \tan^{- 1}\sqrt{\frac{1 + \cos\frac{x}{2}}{1 - \cos\frac{x}{2}}} \right)\$is equal to

A) $- 1/4$
B) 1/4
C) $- 1/2$
D) 1/2
Explanation

(a)
$\frac{d}{dx} = \left( \tan^{- 1}\sqrt{\frac{1 + \cos\frac{x}{2}}{1 - \cos\frac{x}{2}}} \right)\ = \ \frac{d}{dx}\tan^{- 1}\sqrt{\frac{2\cos^{2}\frac{x}{4}}{2\sin^{2}\frac{x}{4}}}$
$= \frac{d}{dx}\ \tan^{- 1}\left| \cot\left( \frac{x}{4} \right) \right|$
$= \frac{d}{dx}\tan^{- 1}\left| \tan\left( \frac{\pi}{2} - \frac{x}{4} \right) \right|$
$= \frac{d}{dx}\left( \frac{\pi}{2} - \frac{x}{4} \right) = \frac{- 1}{4}$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

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