Manipal Engineering Manipal Engineering Solved Paper-2010

  • question_answer
    If\[f(x)={{\log }_{x}}(\log x)\], then\[f(x)\]at\[x=e\]is

    A) \[1/e\]                                 

    B) \[e\]

    C) \[-1/e\]               

    D)        \[0\]

    Correct Answer: A

    Solution :

    We have,\[f(x)={{\log }_{x}}(\log x)=\frac{\log (\log x)}{\log x}\] \[\Rightarrow \]\[f(x)=\frac{\log x\cdot \frac{1}{\log x}\cdot \frac{1}{x}-\log (\log x)\cdot \frac{1}{x}}{{{(\log x)}^{2}}}\]                 \[=\frac{1-\log (\log x)}{x{{(\log x)}^{2}}}\] \[\therefore \]  \[f(e)=\frac{1-\log (\log e)}{e{{(\log e)}^{2}}}=\frac{1}{e}\]


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