If $y=\cot ^{-1}\left(\sqrt{\frac{1-\sin x}{1+\sin x}}\right)$, then $\frac{d y}{d x}=$

If $y=\cot ^{-1}\left(\sqrt{\frac{1-\sin x}{1+\sin x}}\right)$, then $\frac{d y}{d x}=$
  1. $\frac{1}{2}$
  2. $-1$
  3. $\frac{1}{3}$
  4. 1

Solution

$\begin{aligned} y &=\cot ^{-1} \sqrt{\frac{\left(\cos \frac{x}{2}-\sin \frac{x}{2}\right)^{2}}{\left(\cos \frac{x}{2}+\sin \frac{x}{2}\right)^{2}}}=\cot ^{-1}\left(\frac{\cos \frac{x}{2}-\sin \frac{x}{2}}{\cos \frac{x}{2}+\sin \frac{x}{2}}\right) \\ &=\cot ^{-1}\left[\frac{1-\tan \frac{x}{2}}{\left.1+\tan \frac{x}{2}\right)}=\tan ^{-1}\left(\frac{1+\tan \frac{x}{2}}{1-\tan \frac{x}{2}}\right)=\tan ^{-1}\left[\frac{\tan \frac{\pi}{4}+\tan \frac{x}{2}}{1-\tan \frac{\pi}{4} \tan \frac{x}{2}}\right]\right.\\ \therefore \frac{d y}{d x} &=0+\frac{1}{2}=\frac{1}{2} \end{aligned}$

Asked in: MHT CET 2020 (12 Oct Shift 2)

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