JEE Main & Advanced Mathematics Indefinite Integrals Question Bank Integration by Parts

  • question_answer
    \[\int_{{}}^{{}}{{{x}^{2}}\sin 2x}\ dx=\] [IIT 1974]

    A)                 \[\frac{1}{2}{{x}^{2}}\cos 2x+\frac{1}{2}x\sin 2x+\frac{1}{4}\cos 2x+c\] 

    B)                 \[-\frac{1}{2}{{x}^{2}}\cos 2x+\frac{1}{2}x\sin 2x+\frac{1}{4}\cos 2x+c\]

    C)                 \[\frac{1}{2}{{x}^{2}}\cos 2x-\frac{1}{2}x\sin 2x+\frac{1}{4}\cos 2x+c\]

    D)                 None of these

    Correct Answer: B

    Solution :

                    Let \[I=\int_{{}}^{{}}{{{x}^{2}}\sin 2x\,dx}=\frac{-{{x}^{2}}\cos 2x}{2}+\int_{{}}^{{}}{\frac{2x\cos 2x}{2}\,dx}+c\]                         \[=-\frac{{{x}^{2}}\cos 2x}{2}+\frac{x\sin 2x}{2}+\frac{\cos 2x}{4}+c.\]


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