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# Solution for Differentiate Tan − 1 ( 1 − X 1 + X ) with Respect to √ 1 − X 2 , If − 1 < X < 1 ? - CBSE (Commerce) Class 12 - Mathematics

ConceptSimple Problems on Applications of Derivatives

#### Question

Differentiate $\tan^{- 1} \left( \frac{1 - x}{1 + x} \right)$ with respect to $\sqrt{1 - x^2},\text {if} - 1 < x < 1$ ?

#### Solution

$\text { Let, u } = \tan^{- 1} \left( \frac{1 - x}{1 + x} \right)$

$\text { Put x }= \tan\theta$

$\Rightarrow \theta = \tan^{- 1} x$

$\Rightarrow u = \tan^{- 1} \left( \frac{1 - \tan\theta}{1 + \tan\theta} \right)$

$\Rightarrow u = \tan^{- 1} \left[ \tan\left( \frac{\pi}{4} - \theta \right) \right] . . . \left( i \right)$

$\text { Here,}$

$- 1 < x < 1$

$\Rightarrow - 1 < \tan\theta < 1$

$\Rightarrow - \frac{\pi}{4} < \theta < \frac{\pi}{4}$

$\Rightarrow \frac{\pi}{4} > - \theta > \frac{\pi}{4}$

$\Rightarrow - \frac{\pi}{4} < - \theta < \frac{\pi}{4}$

$\Rightarrow 0 < \frac{\pi}{4} - \theta < \frac{\pi}{2}$

$\text { So, from equation } \left( i \right),$

$u = \frac{\pi}{4} - \theta \left[ \text { Since }, \tan^{- 1} \left( \tan\theta \right) = \theta, \text { if } \theta \in \left( - \frac{\pi}{2}, \frac{\pi}{2} \right) \right]$

$\Rightarrow u = \frac{\pi}{4} - \tan^{- 1} x$

Differentiating it with respect to x,

$\frac{du}{dx} = 0 - \left( \frac{1}{1 + x^2} \right)$

$\Rightarrow \frac{du}{dx} = - \frac{1}{1 + x^2} . . . \left( ii \right)$

$\text {And let, v } = \sqrt{1 - x^2}$

Differentiating it with respect to x,

$\frac{dv}{dx} = \frac{1}{2\sqrt{1 - x^2}} \times \frac{d}{dx}\left( 1 - x^2 \right)$

$\Rightarrow \frac{dv}{dx} = \frac{1}{2\sqrt{1 - x^2}}\left( - 2x \right)$

$\Rightarrow \frac{dv}{dx} = \frac{- x}{\sqrt{1 - x^2}} . . . \left( iii \right)$

$\text { Dividing equation }\left( ii \right) by \left( iii \right),$

$\frac{\frac{du}{dx}}{\frac{dv}{dx}} = - \frac{1}{1 + x^2} \times \frac{\sqrt{1 - x^2}}{- x}$

$\therefore \frac{du}{dv} = \frac{\sqrt{1 - x^2}}{x\left( 1 + x^2 \right)}$

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Solution for question: Differentiate Tan − 1 ( 1 − X 1 + X ) with Respect to √ 1 − X 2 , If − 1 < X < 1 ? concept: Simple Problems on Applications of Derivatives. For the courses CBSE (Commerce), CBSE (Arts), PUC Karnataka Science, CBSE (Science)
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