JEE Main & Advanced Mathematics Definite Integration Question Bank Summation of series by Definite Integration, Gamma function, Leibnitz's rule

  • question_answer
    \[\int_{0}^{\infty }{\frac{x\,dx}{(1+x)(1+{{x}^{2}})}}=\]

    A)                 \[\frac{\pi }{4}\]              

    B)                 \[\frac{\pi }{3}\]

    C)                 \[\frac{\pi }{6}\]              

    D)                 None of these

    Correct Answer: A

    Solution :

                       \[I=\int_{0}^{\infty }{\frac{xdx}{(1+x)(1+{{x}^{2}})}}\]            Put \[x=\tan \theta \], we get                 \[I=\int_{0}^{\pi /2}{\frac{\tan \theta }{1+\tan \theta }d\theta =\int_{0}^{\pi /2}{\frac{\sin \theta }{\cos \theta +\sin \theta }d\theta =\frac{\pi }{4}}}\].


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