If $\mathrm{y}=\tan ^{-1}\left[\frac{x-\sqrt{1-x^{2}}}{x+\sqrt{1-x^{2}}}\right]$, then $\left(\frac{d y}{d…

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

Solution

Given $y=\tan ^{-1}\left[\frac{x-\sqrt{1-x^{2}}}{x+\sqrt{1-x^{2}}}\right]$ Put $x=\cos \theta \Rightarrow \theta=\cos ^{-1} x$ $y=\tan ^{-1}\left[\frac{\cos \theta-\sin \theta}{\cos \theta+\sin \theta}\right]=\tan ^{-1}\left[\frac{1-\tan \theta}{1+\tan \theta}\right]$ $\quad=\tan ^{-1}\left[\tan \left(\frac{\pi}{4}-\theta\right)\right]=\frac{\pi}{4}-\theta$ $\therefore \frac{d y}{d x}=\frac{\pi}{4}-\cos ^{-1} x$ $\begin{aligned} y &=\frac{1}{\sqrt{1-x^{2}}} \\ y &=\frac{1}{\sqrt{1-x^{2}}} \end{aligned}$

Asked in: MHT CET 2020 (15 Oct Shift 2)

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