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If $y=x^{\tan^{-1}x}$, then $\dfrac{dy}{dx}$ equals
A$x^{\tan^{-1}x}\left(\dfrac{\tan^{-1}x}{x}+\dfrac{\log x}{1+x^2}\right)$
B$x^{\tan^{-1}x}\left(\dfrac{1}{x}+\dfrac{1}{1+x^2}\right)$
C$x^{\tan^{-1}x}\left(\tan^{-1}x+\log x\right)$
D$x^{\tan^{-1}x}\left(\dfrac{\tan^{-1}x}{x}-\dfrac{\log x}{1+x^2}\right)$
Answer & Solution
Correct answer: A. $x^{\tan^{-1}x}\left(\dfrac{\tan^{-1}x}{x}+\dfrac{\log x}{1+x^2}\right)$
For a variable base and variable exponent, logarithmic differentiation is convenient. Write $\log y=\tan^{-1}x\cdot \log x$. Differentiating, $\frac{1}{y}\frac{dy}{dx}=\frac{\tan^{-1}x}{x}+\frac{\log x}{1+x^2}$. Multiplying by $y=x^{\tan^{-1}x}$ gives option A.
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