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

  • question_answer
    \[\int_{0}^{\pi /2}{\frac{{{\sin }^{3/2}}x\,dx}{{{\cos }^{3/2}}x+{{\sin }^{3/2}}x}}=\] [Roorkee 1989; BIT Ranchi 1989]

    A)                 0             

    B)                 \[\pi \]

    C)                 \[\pi /2\]             

    D)                 \[\pi /4\]

    Correct Answer: D

    Solution :

               Let \[I=\int_{0}^{\pi /2}{\frac{{{\sin }^{3/2}}x\,dx}{{{\cos }^{3/2}}x+{{\sin }^{3/2}}x}}\]                       ?..(i)                             = \[\int_{0}^{\pi /2}{\frac{{{\sin }^{3/2}}\left( \frac{\pi }{2}-x \right)}{{{\cos }^{3/2}}\left( \frac{\pi }{2}-x \right)+{{\sin }^{3/2}}\left( \frac{\pi }{2}-x \right)}dx}\]                             = \[\int_{0}^{\pi /2}{\frac{{{\cos }^{3/2}}x\,dx}{{{\sin }^{3/2}}x+{{\cos }^{3/2}}x}}\]                             .....(ii)                                 Adding (i) and (ii), we get \[I=\frac{1}{2}\int_{0}^{\pi /2}{1dx=\frac{1}{2}[x]_{0}^{\pi /2}=\frac{\pi }{4}}\].


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