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

  • question_answer
    \[\int_{0}^{\pi /2}{\frac{\sqrt{\cos x}}{\sqrt{\sin x}+\sqrt{\cos x}}\,dx=}\]             [MNR 1989; UPSEAT 2002]

    A)                 0             

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

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

    D)                 None of these

    Correct Answer: C

    Solution :

               Let \[I=\int_{0}^{\pi /2}{\,\,\frac{\sqrt{\cos x}}{\sqrt{\sin x}+\sqrt{\cos x}}dx}\]      .....(i)            and \[I=\int_{0}^{\pi /2}{\frac{\sqrt{\cos \left( \frac{\pi }{2}-x \right)}}{\sqrt{\sin \left( \frac{\pi }{2}-x \right)}+\sqrt{\cos \left( \frac{\pi }{2}-x \right)}}dx}\]                  \[I=\int_{0}^{\pi /2}{\frac{\sqrt{\sin x}}{\sqrt{\cos x+}\sqrt{\sin x}}}\,dx\]          ?..(ii)            Adding (i) and (ii), we get                  \[2I=\int_{0}^{\pi /2}{(1)dx=\frac{\pi }{2}\Rightarrow I=\frac{\pi }{4}}\].


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