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# If Y = Cos − 1 { 2 X − 3 √ 1 − X 2 √ 13 } , Find D Y D X ? - CBSE (Arts) Class 12 - Mathematics

ConceptSimple Problems on Applications of Derivatives

#### Question

If $y = \cos^{- 1} \left\{ \frac{2x - 3 \sqrt{1 - x^2}}{\sqrt{13}} \right\}, \text{ find } \frac{dy}{dx}$ ?

#### Solution

$\text{ Let y }= \cos^{- 1} \left\{ \frac{2x - 3\sqrt{1 - x^2}}{\sqrt{13}} \right\}$

$\text{ Put, x }= \cos\theta$

$y = \cos^{- 1} \left\{ \frac{2\cos\theta - 3\sqrt{1 - \cos^2 \theta}}{\sqrt{13}} \right\}$

$y = \cos^{- 1} \left\{ \frac{2\cos\theta - 3\sin\theta}{\sqrt{13}} \right\}$

$y = \cos^{- 1} \left\{ \cos\theta\left( \frac{2}{\sqrt{13}} \right) + \sin\theta\left( \frac{3}{\sqrt{13}} \right) \right\}$

$\text{ Let } \cos\phi = \frac{2}{\sqrt{13}} \text{ and }\sin\phi = \frac{3}{\sqrt{13}}$

$y = \cos^{- 1} \left\{ \cos\theta\cos\phi + \sin\theta \sin\phi \right\}$

$y = \cos^{- 1} \left\{ \cos\left( \theta - \phi \right) \right\} . . . \left( i \right)$

$y = \left( \theta - \phi \right)$

$y = \cos^{- 1} x - \phi$

$\text{ Differentiating it with respect to x },$

$\frac{d y}{d x} = - \frac{1}{\sqrt{1 - x^2}} + 0$

$\frac{d y}{d x} = - \frac{1}{\sqrt{1 - x^2}}$

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Solution If Y = Cos − 1 { 2 X − 3 √ 1 − X 2 √ 13 } , Find D Y D X ? Concept: Simple Problems on Applications of Derivatives.
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