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JEE Main 2023
Differentiation
Differentiation
Hard

Question

If logey=3sin1x\log _e y=3 \sin ^{-1} x, then (1x2)yxy(1-x^2) y^{\prime \prime}-x y^{\prime} at x=12x=\frac{1}{2} is equal to

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Solution

logey=3sin1xy=e3sin1xdydx=e3sin1x31x2\begin{aligned} &\log _e y=3 \sin ^{-1} x\\ &\begin{aligned} & y=e^{3 \sin ^{-1} x} \\ & \frac{d y}{d x}=e^{3 \sin ^{-1} x} \cdot \frac{3}{\sqrt{1-x^2}} \end{aligned} \end{aligned} 1x2dydx=3y\sqrt{1-x^2} \frac{d y}{d x}=3 y Again differentiate 1x2y2x21x2y=3y(1x)2yxy=3y(1x2)\begin{aligned} & \sqrt{1-x^2} \cdot y^{\prime \prime}-\frac{2 x}{2 \sqrt{1-x^2}} y^{\prime}=3 y^{\prime} \\ & (1-x)^2 y^{\prime \prime}-x y^{\prime}=3 y^{\prime}\left(\sqrt{1-x^2}\right) \end{aligned} So value of 3y(1x2)3 y^{\prime}\left(\sqrt{1-x^2}\right) at x=12x=\frac{1}{2} 331x2esin1x(1x2)=9e3π6=9eπ2\begin{aligned} & 3 \cdot \frac{3}{\sqrt{1-x^2}} e^{\sin ^{-1} x}\left(\sqrt{1-x^2}\right) \\ & =9 e^{3 \frac{\pi}{6}}=9 e^{\frac{\pi}{2}} \end{aligned}

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