JEE Main & Advanced Mathematics Definite Integration Question Bank Properties of Definite Integration

  • question_answer
    \[\int_{0}^{\pi /2}{x\cot x\,dx}\] equals                                                [RPET 1997]

    A)                 \[-\frac{\pi }{2}\log 2\] 

    B)                 \[\frac{\pi }{2}\log 2\]

    C)                 \[\pi \log 2\]      

    D)                 \[-\pi \log 2\]

    Correct Answer: B

    Solution :

               \[I=\int_{0}^{\pi /2}{x\cot x\,dx}\]                    Integrating by parts, we get \[[x(\log \sin x)]_{0}^{\pi /2}-\int_{0}^{\pi /2}{\log \sin x\,dx}\]                                 \[I=-\left( -\frac{\pi }{2}\log 2 \right)=\frac{\pi }{2}\log 2\].


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