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If cos⁡y=xcos⁡(a+y)\cos y = x\cos(a+y), then dydx=\frac{dy}{dx} =

Solution

✅ Correct Option: 1

From x=cos⁡ycos⁡(a+y)x = \frac{\cos y}{\cos(a+y)}, differentiate w.r.t. yy:

dxdy=−sin⁡ycos⁡(a+y)+cos⁡ysin⁡(a+y)cos⁡2(a+y)=sin⁡acos⁡2(a+y)\frac{dx}{dy} = \frac{-\sin y \cos(a+y) + \cos y \sin(a+y)}{\cos^2(a+y)} = \frac{\sin a}{\cos^2(a+y)}.

So dydx=cos⁡2(a+y)sin⁡a\frac{dy}{dx} = \frac{\cos^2(a+y)}{\sin a}.

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