JEE Main & Advanced Mathematics Applications of Derivatives Question Bank Maxima and Minima

  • question_answer
    Maximum value of \[{{\left( \frac{1}{x} \right)}^{x}}\] is  [DCE 1999; Karnataka CET 1999; UPSEAT 2003]

    A)            \[{{(e)}^{e}}\]                     

    B)            \[{{(e)}^{e}}\]

    C)            \[{{(e)}^{-e}}\]

    D)            \[{{\left( \frac{1}{e} \right)}^{e}}\]

    Correct Answer: B

    Solution :

               \[f(x)={{\left( \frac{1}{x} \right)}^{x}}\]Þ \[f'(x)={{\left( \frac{1}{x} \right)}^{x}}\left( \log \frac{1}{x}-1 \right)\]                    \[f'(x)=0\Rightarrow \log \frac{1}{x}=1=\log e\Rightarrow \frac{1}{x}=e\Rightarrow x=\frac{1}{e}\]                    Therefore maximum value of function is \[{{e}^{1/e}}\].


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