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

  • question_answer
    \[\int_{{}}^{{}}{x{{\sin }^{2}}x\ dx=}\]    [BIT Ranchi 1977; IIT 1972]

    A)                 \[\frac{{{x}^{2}}}{4}+\frac{x}{4}\sin 2x+\frac{1}{8}\cos 2x+c\]

    B)                 \[\frac{{{x}^{2}}}{4}-\frac{x}{4}\sin 2x+\frac{1}{8}\cos 2x+c\]

    C)                 \[\frac{{{x}^{2}}}{4}+\frac{x}{4}\sin 2x-\frac{1}{8}\cos 2x+c\]     

    D)                 \[\frac{{{x}^{2}}}{4}-\frac{x}{4}\sin 2x-\frac{1}{8}\cos 2x+c\]

    Correct Answer: D

    Solution :

                    \[\int_{{}}^{{}}{x{{\sin }^{2}}x\,dx}=\int_{{}}^{{}}{x\,.\,\frac{(1-\cos 2x)}{2}\,dx}\]                 \[=\frac{1}{2}\left[ \int_{{}}^{{}}{x\,dx}-\int_{{}}^{{}}{x\,.\,\cos 2x\,dx} \right]=\frac{{{x}^{2}}}{4}-\frac{x}{4}\sin 2x-\frac{1}{8}\cos 2x+c\].


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