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

  • question_answer
    If \[\int_{{}}^{{}}{\ln ({{x}^{2}}+x)dx=x\ln ({{x}^{2}}+x)+A}\], then \[A=\] [MP PET 1992]

    A)                 \[2x+\ln (x+1)+\]constant

    B)                 \[2x-\ln (x+1)+\]constant

    C)                 Constant

    D)                 None of these

    Correct Answer: D

    Solution :

                    \[\int_{{}}^{{}}{\log ({{x}^{2}}+x)\,dx}=\int_{{}}^{{}}{\log x\,dx}+\int_{{}}^{{}}{\log (x+1)\,dx}\]                 \[=x\log x-x+x\log (x+1)-x+\log (x+1)\]                 \[=x\left\{ (\log x+\log (x+1) \right\}-2x+\log (x+1)\]                 \[=x\log ({{x}^{2}}+x)-2x+\log (x+1)\]                 Equating it to the given integration, we get                 \[A=-2x+\log (x+1)\].


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