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# If X Sin ( a + Y ) + Sin a Cos ( a + Y ) = 0 Prove that D Y D X = Sin 2 ( a + Y ) Sin a ? - CBSE (Arts) Class 12 - Mathematics

ConceptSimple Problems on Applications of Derivatives

#### Question

If $x \sin \left( a + y \right) + \sin a \cos \left( a + y \right) = 0$ Prove that $\frac{dy}{dx} = \frac{\sin^2 \left( a + y \right)}{\sin a}$ ?

#### Solution

$\text{ We have, } x\sin\left( a + y \right) + \sin a\cos\left( a + y \right) = 0$

Differentiate with respect to x,

$\Rightarrow \frac{d}{dx}\left[ x \sin\left( a + y \right) \right] + \frac{d}{dx}\left[ \sin a \cos\left( a + y \right) \right] = 0$

$\Rightarrow \left[ x\frac{d}{dx}\sin \left( a + y \right) + \sin\left( a + y \right)\frac{d}{dx}\left( x \right) \right] + \sin a\frac{d}{dx}\cos\left( a + y \right) = 0$

$\Rightarrow \left[ x \cos\left( a + y \right)\frac{d}{dx}\left( a + y \right) + \sin\left( a + y \right)\left( 1 \right) \right] + \sin a\left[ - \sin\left( a + y \right)\frac{d}{dx}\left( a + y \right) \right] = 0$

$\Rightarrow x \cos\left( a + y \right)\frac{d y}{d x} + \sin\left( a + y \right) - \sin a\sin\left( a + y \right)\frac{d y}{d x} = 0$

$\Rightarrow \frac{d y}{d x}\left[ x \cos\left( a + y \right) - \sin a \sin\left( a + y \right) \right] = - \sin\left( a + y \right)$

$\Rightarrow \frac{d y}{d x}\left[ - \sin a\frac{\cos^2 \left( a + y \right)}{\sin\left( a + y \right)} - \sin a \sin\left( a + y \right) \right] = - \sin\left( a + y \right) \left[ \because x = - \sin a\frac{\cos\left( a + y \right)}{\sin\left( a + y \right)} \right]$

$\Rightarrow - \frac{d y}{d x}\left[ \frac{\sin a \cos^2 \left( a + y \right) + \sin a \sin^2 \left( a + y \right)}{\sin\left( a + y \right)} \right] = - \sin\left( a + y \right)$

$\Rightarrow \frac{d y}{d x} = \sin\left( a + y \right)\left[ \frac{\sin\left( a + y \right)}{\sin a\left\{ \cos^2 \left( a + y \right) + \sin^2 \left( a + y \right) \right\}} \right]$

$\Rightarrow \frac{d y}{d x} = \frac{\sin^2 \left( a + y \right)}{\sin a}$

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Solution If X Sin ( a + Y ) + Sin a Cos ( a + Y ) = 0 Prove that D Y D X = Sin 2 ( a + Y ) Sin a ? Concept: Simple Problems on Applications of Derivatives.
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