Derivative of $\tan ^{-1}\left(\frac{\sqrt{1+x^2}-\sqrt{1-x^2}}{\sqrt{1+x^2}+\sqrt{1-x^2}}\right)$ w.r.t.…

Derivative of $\tan ^{-1}\left(\frac{\sqrt{1+x^2}-\sqrt{1-x^2}}{\sqrt{1+x^2}+\sqrt{1-x^2}}\right)$ w.r.t. $\cos ^{-1} x^2$ is
  1. $-\frac{1}{2}$
  2. $-1$
  3. $\frac{1}{2}$
  4. $1$

Solution

Let $y=\tan ^{-1}\left(\frac{\sqrt{1+x^2}-\sqrt{1-x^2}}{\sqrt{1+x^2}+\sqrt{1-x^2}}\right)$ and $\mathrm{z}=\cos ^{-1}\left(x^2\right)$ Put $x^2=\cos 2 \theta \Rightarrow \theta=\frac{1}{2} \cos ^{-1} x^2$ $\begin{aligned} \therefore \quad y & =\tan ^{-1}\left(\frac{\sqrt{1+\cos 2 \theta}-\sqrt{1-\cos 2 \theta}}{\sqrt{1+\cos 2 \theta}+\sqrt{1-\cos 2 \theta}}\right) \\ \Rightarrow y & =\tan ^{-1}\left(\frac{\cos \theta-\sin \theta}{\cos \theta+\sin \theta}\right) \\ \Rightarrow y & =\tan ^{-1}\left(\frac{1-\tan \theta}{1+\tan \theta}\right) \\ \Rightarrow y & =\tan ^{-1}\left(\tan \left(\frac{\pi}{4}-\theta\right)\right) \\ \Rightarrow y & =\frac{\pi}{4}-\frac{1}{2} \cos ^{-1} x^2 \\ \Rightarrow y & =\frac{\pi}{4}-\frac{1}{2} \mathrm{z} \\ \therefore \quad \frac{\mathrm{dy}}{\mathrm{dz}} & =-\frac{1}{2} \end{aligned}$

Asked in: MHT CET 2023 (11 May Shift 1)

Practice more Differentiation questions on Aicharya