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

  • question_answer
    If \[f(x)={{\log }_{x}}(\log x),\]then \[f'(x)\]at \[x=e\]is [IIT 1985; RPET 2000; MP PET 2000; Karnataka CET 2002; Pb. CET 2002]

    A)            e

    B)            \[\frac{1}{e}\]

    C)            1

    D)            None of these

    Correct Answer: B

    Solution :

               \[f(x)={{\log }_{x}}(\log x)=\frac{\log (\log x)}{\log x}\]            Þ \[f'(x)=\frac{\frac{1}{x}-\frac{1}{x}\log (\log x)}{{{(\log x)}^{2}}}\Rightarrow f'(e)=\frac{\frac{1}{e}-0}{1}=\frac{1}{e}\].


You need to login to perform this action.
You will be redirected in 3 sec spinner