JEE Main & Advanced Mathematics Differentiation Question Bank Derivative at a point Standard Differentiation

  • question_answer
    If \[f(x)=x{{\tan }^{-1}}x\], then \[f'(1)\]=                                                    [IIT 1979]

    A)            \[1+\frac{\pi }{4}\]

    B)            \[\frac{1}{2}+\frac{\pi }{4}\]

    C)            \[\frac{1}{2}-\frac{\pi }{4}\]

    D)            2

    Correct Answer: B

    Solution :

               \[f(x)=x{{\tan }^{-1}}x\]            Differentiating w.r.t x, we get \[f'(x)=x\frac{1}{1+{{x}^{2}}}+{{\tan }^{-1}}x\]            Now put \[x=1\], then \[f'(1)=\frac{1}{2}+{{\tan }^{-1}}(1)=\frac{\pi }{4}+\frac{1}{2}\].


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