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

  • question_answer
    \[\int_{{}}^{{}}{\frac{x-\sin x}{1-\cos x}dx=}\]        [AISSE 1989]

    A)                 \[x\cot \frac{x}{2}+c\]

    B)                 \[-x\cot \frac{x}{2}+c\]

    C)                 \[\cot \frac{x}{2}+c\]

    D)                 None of these

    Correct Answer: B

    Solution :

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


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