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

  • question_answer
    \[\int_{0}^{a}{{{x}^{4}}\sqrt{{{a}^{2}}-{{x}^{2}}}}\,dx=\]

    A)                 \[\frac{\pi }{32}\]            

    B)                 \[\frac{\pi }{32}{{a}^{6}}\]

    C)                 \[\frac{\pi }{16}{{a}^{6}}\]           

    D)                 \[\frac{\pi }{8}{{a}^{6}}\]

    Correct Answer: B

    Solution :

                       Put \[x=a\sin \theta \Rightarrow dx=a\cos \theta \,\,d\theta \]            Now \[\int_{0}^{a}{{{x}^{4}}\sqrt{{{a}^{2}}-{{x}^{2}}}}dx={{a}^{6}}\int_{0}^{\pi /2}{{{\sin }^{4}}\theta \cos \theta \cos \theta \,d\theta }\]                    \[={{a}^{6}}\int_{0}^{\pi /2}{{{\sin }^{4}}\theta {{\cos }^{2}}\theta \,d\theta }\]\[={{a}^{6}}\frac{\Gamma \left( \frac{5}{2} \right).\Gamma \left( \frac{3}{2} \right)}{2\Gamma 4}=\frac{\pi }{32}{{a}^{6}}\],  (Using gamma function).


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