RAJASTHAN ­ PET Rajasthan PET Solved Paper-2011

  • question_answer
    The integral \[\int_{-1/2}^{1/2}{\left\{ [x]+\log \left( \frac{1+x}{1-x} \right) \right\}dx}=?\] Where\[[.]\]is the greatest integer function.

    A)  \[-1/2\]           

    B)  0

    C)  1             

    D)  \[2\log (1/2)\]

    Correct Answer: A

    Solution :

     \[\int_{-1/2}^{1/2}{\left\{ [x]+\log \left( \frac{1+x}{1-x} \right) \right\}}dx\] \[=\int_{-1/2}^{1/2}{[x]dx+\int_{-1/2}^{1/2}{\log \left( \frac{1+x}{1-x} \right)}}dx\] \[=\int_{-1/2}^{1/2}{[x]dx+0}\] \[\left[ \because \log \left( \frac{1+x}{1-x} \right) \right.\]is an odd function of\[x\] \[\Rightarrow \] \[\left. \int_{-1/2}^{1/2}{\log \left( \frac{1+x}{1-x} \right)dx}=0 \right]\] \[=\int_{-1/2}^{0}{[x]}\,dx+\int_{0}^{1/2}{[x]}\,dx\] \[=[-x]_{-1/2}^{0}+0=0-1/2=-1/2\]


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