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

  • question_answer
    \[\int_{{}}^{{}}{{{x}^{3}}{{e}^{{{x}^{2}}}}dx=}\]      [MNR 1980]

    A)                 \[\frac{1}{2}({{x}^{2}}+1){{e}^{{{x}^{2}}}}+c\]

    B)                 \[({{x}^{2}}+1){{e}^{{{x}^{2}}}}+c\]

    C)                 \[\frac{1}{2}({{x}^{2}}-1){{e}^{{{x}^{2}}}}+c\]

    D)                 \[({{x}^{2}}-1){{e}^{{{x}^{2}}}}+c\]

    Correct Answer: C

    Solution :

                    Put \[{{x}^{2}}=t\Rightarrow 2x\,dx=dt,\] then \[\int_{{}}^{{}}{{{x}^{3}}{{e}^{{{x}^{2}}}}dx}=\frac{1}{2}\int_{{}}^{{}}{t{{e}^{t}}dt}\]                                                    \[=\frac{1}{2}\left[ t{{e}^{t}}-{{e}^{t}} \right]+c\]\[=\frac{1}{2}{{e}^{{{x}^{2}}}}({{x}^{2}}-1)+c.\]


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