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

  • question_answer
    The value of \[\int_{\,0}^{\,\pi }{\,\left| \,{{\sin }^{3}}\theta \, \right|\,d\theta }\] is                      [UPSEAT 2003]

    A)                 0             

    B)                 3/8

    C)                 4/3        

    D)                 \[\pi \]

    Correct Answer: C

    Solution :

               \[I=\int_{0}^{\pi }{|{{\sin }^{3}}\theta |}\,d\theta \]            Since \[\sin \theta \] is positive in interval \[(0,\pi )\]            \[\therefore I=\int_{0}^{\pi }{{{\sin }^{3}}\theta \,d\theta =\int_{0}^{\pi }{\sin \theta (1-{{\cos }^{2}}\theta )\,\,d\theta }}\]             \[=\int_{0}^{\pi }{\sin \theta \,d\theta +\int_{0}^{\pi }{(-\sin \theta )\,{{\cos }^{2}}\theta \,d\theta }}\]                      \[=[-\cos \theta ]_{0}^{\pi }+\left( \frac{{{\cos }^{3}}\theta }{3} \right)_{0}^{\pi }=\frac{4}{3}\].


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