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

  • question_answer
    The value of \[\int_{\,0}^{\,\pi /2}{{{\left( \sqrt{\sin \theta }\cos \theta  \right)}^{3}}d\theta }\] is           [AMU 1999]

    A)                 2/9        

    B)                 2/15

    C)                 8/45      

    D)                 5/2

    Correct Answer: C

    Solution :

                       \[\int_{\,0}^{\,\pi /2}{{{(\sqrt{\sin \theta }\cos \theta )}^{3}}\,\,d\theta =\int_{\,0}^{\,\pi /2}{{{\sin }^{3/2}}\theta {{\cos }^{3}}\theta \,\,d\theta }}\]            Applying gamma function,            \[\int_{0}^{\pi /2}{{{\sin }^{3/2}}\theta {{\cos }^{3}}\theta d\theta }\]\[=\frac{\Gamma \left( \frac{\frac{3}{2}+1}{2} \right)\Gamma \left( \frac{3+1}{2} \right)}{2\Gamma \left( \frac{\frac{3}{2}+3+2}{2} \right)}\]                                                      \[=\frac{\Gamma (5/4)\,\,\Gamma \,2}{2\Gamma \,(13/4)}\]\[=\frac{\Gamma \,\left( \frac{5}{4} \right)}{2.\frac{9}{4}.\frac{5}{4}.\Gamma \left( \frac{5}{4} \right)}\]\[=\frac{8}{45}\].


You need to login to perform this action.
You will be redirected in 3 sec spinner