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Need solution for RD Sharma maths class 12 chapter 10 Differentiation exercise Very short answers question 15

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Answer:

    -1

Hint:

\begin{aligned} &\text { Using (1) } 1-\cos 2 x=2 \sin ^{2} x\\ &\text { (2) } 1+\cos 2 x=2 \cos ^{2} x \end{aligned}

Given:

y=\tan ^{-1}\left(\sqrt{\frac{1-\cos 2 x}{1+\cos 2 x}}\right)

Solution:  

\begin{aligned} &y=\tan ^{-1}\left(\sqrt{\frac{1-\cos 2 x}{1+\cos 2 x}}\right) \\\\ &y=\tan ^{-1}\left(\sqrt{\frac{2 \sin ^{2} x}{2 \cos ^{2} x}}\right) \end{aligned}

Using

\begin{aligned} &1-\cos 2 x=2 \sin ^{2} x \\\\ &1+\cos 2 x=2 \cos ^{2} x \\\\ &y=\tan ^{-1}\left(\sqrt{\tan ^{2} x}\right) \end{aligned}

\begin{aligned} &y=\tan ^{-1}(-\tan x)\left[-\frac{\pi}{2}<x<0\right] \\\\ &y=-x \quad\left[\because \tan ^{-1}(\tan x)=x\right] \end{aligned}

Differentiate it w.r.t x, we get

\begin{aligned} &\frac{d y}{d x}=\frac{d(-x)}{d x} \\\\ &\frac{d y}{d x}=-1 \text { for } x \in\left(-\frac{\pi}{2}, 0\right) \end{aligned}

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