RAJASTHAN ­ PET Rajasthan PET Solved Paper-2001

  • question_answer
    \[\int_{0}^{1}{\frac{{{\tan }^{-1}}xdx}{1+{{x}^{2}}}}\]is equal to

    A)  \[\frac{\pi }{4}\]

    B)  \[\frac{\pi }{8}\]

    C)  \[\frac{{{\pi }^{2}}}{16}\]

    D)  \[\frac{{{\pi }^{2}}}{32}\]

    Correct Answer: D

    Solution :

     Let \[I=\int_{0}^{1}{\frac{{{\tan }^{-1}}x}{1+{{x}^{2}}}}dx\] Let \[{{\tan }^{-1}}x=t\] \[\Rightarrow \] \[\frac{1}{1+{{x}^{2}}}dx=dt\] when \[x=0,\text{ }t=0\] and      \[x=1,t=\frac{\pi }{4}\] \[\therefore \] \[I=\int_{0}^{\pi /4}{t\,dt}\] \[=\left( \frac{{{t}^{2}}}{2} \right)_{0}^{\frac{\pi }{4}}=\frac{{{\pi }^{2}}}{16\times 2}\] \[=\frac{{{\pi }^{2}}}{32}\]


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