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JEE Main 2023
Differentiation
Differentiation
Medium

Question

Suppose f(x)=(2x+2x)tanxtan1(x2x+1)(7x2+3x+1)3f(x)=\frac{\left(2^x+2^{-x}\right) \tan x \sqrt{\tan ^{-1}\left(x^2-x+1\right)}}{\left(7 x^2+3 x+1\right)^3}. Then the value of f(0)f^{\prime}(0) is equal to

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Solution

f(0)=limh0f(h)f(0)h=limh0(2h+2h)tanhtan1(h2h+1)0(7h2+3h+1)3h=π\begin{aligned} & f^{\prime}(0)=\lim _{h \rightarrow 0} \frac{f(h)-f(0)}{h} \\ & =\lim _{h \rightarrow 0} \frac{\left(2^h+2^{-h}\right) \tan h \sqrt{\tan ^{-1}\left(h^2-h+1\right)}-0}{\left(7 h^2+3 h+1\right)^3 h} \\ & =\sqrt{\pi} \end{aligned}

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