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

  • question_answer
    \[\int{{{x}^{3}}\log x\,\,dx=}\]   [Karnataka CET 2002]

    A)                 \[\frac{{{x}^{4}}\log x}{4}+c\]

    B)                 \[\frac{1}{16}[4{{x}^{4}}\log x-{{x}^{4}}]+c\]

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

    D)  \[\frac{1}{16}[4{{x}^{4}}\log x+{{x}^{4}}]+c\]

    Correct Answer: B

    Solution :

                    \[I=\int{{{x}^{3}}\log x\,dx}\]\[=\frac{{{x}^{4}}}{4}\log x-\int{\frac{{{x}^{4}}}{4}\frac{1}{x}dx+c}\]                    \[=\frac{{{x}^{4}}}{4}\log x-\int{\frac{{{x}^{3}}}{4}dx\,=\,\frac{{{x}^{4}}}{4}\log x-\frac{{{x}^{4}}}{16}+c}\]                    \[=\frac{1}{16}[4{{x}^{4}}\log x-{{x}^{4}}]+c\].


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