JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2009

  • question_answer
        If\[f(x)=|{{\log }_{e}}|x||,\]then\[{{f}_{0}}(x)\]equals

    A)  \[\frac{1}{|x|},x\ne 0\]

    B)  \[\frac{1}{x}\]for \[|x|>1\]and\[\frac{-1}{x}\]for \[|x|<1\]

    C)  \[\frac{-1}{x}\]for \[|x|>1\]and \[\frac{1}{x}\]for \[|x|<1\]

    D)  \[\frac{1}{x}\]for\[x>0\]and\[-\frac{1}{x}\]for \[x<0\]

    Correct Answer: B

    Solution :

                    For\[x>1,\]we have \[f(x)=|\log |x||=\log x\to f(x)=\frac{1}{x}\] For\[x<-1,\]we have \[f(x)=|\log |x||=\log (-x)\Rightarrow f(x)=\frac{1}{x}\] For\[0<x<1,\]we have \[f(x)=|\log |x||=-\log x\Rightarrow f(x)=\frac{-1}{x}\] For\[-1<x<0,\]we have \[f(x)=-\log (-x)\Rightarrow f(x)=\frac{1}{x}\] Hence, \[f(x)=\left\{ \begin{matrix}    \frac{1}{x}, & |x|>1  \\    -\frac{1}{x}, & |x|<1  \\ \end{matrix} \right.\]


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