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If y=xsin⁡yy = x\sin y, then dydx\frac{dy}{dx} is:

Solution

✅ Correct Option: 2

Given the equation y=xsin⁡yy = x\sin y, where yy appears on both sides. Since yy cannot be isolated, implicit differentiation is needed.


Differentiating both sides with respect to xx:

ddx(y)=ddx(xsin⁡y)\frac{d}{dx}(y) = \frac{d}{dx}(x \sin y)

For the right side, applying the product rule to xsin⁡yx \sin y:

dydx=x⋅ddx(sin⁡y)+ddx(x)⋅sin⁡y\frac{dy}{dx} = x \cdot \frac{d}{dx}(\sin y) + \frac{d}{dx}(x) \cdot \sin y

dydx=x⋅cos⁡y⋅dydx+1⋅sin⁡y\frac{dy}{dx} = x \cdot \cos y \cdot \frac{dy}{dx} + 1 \cdot \sin y

dydx=sin⁡y+xcos⁡y⋅dydx\frac{dy}{dx} = \sin y + x\cos y \cdot \frac{dy}{dx}


Collecting all terms with dydx\frac{dy}{dx} on the left side:

dydx−xcos⁡y⋅dydx=sin⁡y\frac{dy}{dx} - x\cos y \cdot \frac{dy}{dx} = \sin y

dydx(1−xcos⁡y)=sin⁡y\frac{dy}{dx}(1 - x\cos y) = \sin y

dydx=sin⁡y1−xcos⁡y\frac{dy}{dx} = \frac{\sin y}{1 - x\cos y}


From the original equation y=xsin⁡yy = x\sin y:

x=ysin⁡yx = \frac{y}{\sin y}

Substituting into the expression for dydx\frac{dy}{dx}:

dydx=sin⁡y1−ysin⁡y⋅cos⁡y\frac{dy}{dx} = \frac{\sin y}{1 - \frac{y}{\sin y} \cdot \cos y}

dydx=sin⁡y1−ycos⁡ysin⁡y\frac{dy}{dx} = \frac{\sin y}{1 - \frac{y\cos y}{\sin y}}

dydx=sin⁡ysin⁡y−ycos⁡ysin⁡y\frac{dy}{dx} = \frac{\sin y}{\frac{\sin y - y\cos y}{\sin y}}

dydx=sin⁡y⋅sin⁡ysin⁡y−ycos⁡y\frac{dy}{dx} = \frac{\sin y \cdot \sin y}{\sin y - y\cos y}

dydx=sin⁡2ysin⁡y−ycos⁡y\frac{dy}{dx} = \frac{\sin^2 y}{\sin y - y\cos y}

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