JEE Main & Advanced Mathematics Definite Integration Question Bank Fundamental definite integration, Definite integration by substitution

  • question_answer
     \[\int_{0}^{1/2}{\frac{x{{\sin }^{-1}}x}{\sqrt{1-{{x}^{2}}}}\,dx=}\]                                            [IIT 1984]

    A)                 \[\frac{1}{2}+\frac{\sqrt{3}\pi }{12}\]     

    B)                 \[\frac{1}{2}-\frac{\sqrt{3}\pi }{12}\]

    C)                 \[\frac{1}{2}-\frac{\sqrt{3\pi }}{12}\]      

    D)                 None of these

    Correct Answer: B

    Solution :

               Put \[t={{\sin }^{-1}}x\Rightarrow dt=\frac{1}{\sqrt{1-{{x}^{2}}}}dx,\] then                    \[\int_{0}^{1/2}{\frac{x{{\sin }^{-1}}x}{\sqrt{1-{{x}^{2}}}}dx=\int_{0}^{\pi /6}{\,\,t\sin t\,dt}}\]\[=[-t\cos t+\sin t]_{0}^{\pi /6}\]                                                 \[=\left[ -\frac{\pi }{6}.\frac{\sqrt{3}}{2}+\frac{1}{2} \right]=\left[ \frac{1}{2}-\frac{\sqrt{3}\pi }{12} \right]\].


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