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

  • question_answer
    \[\int_{{}}^{{}}{\frac{3{{x}^{2}}}{{{x}^{6}}+1}dx=}\] [MNR 1981; MP PET 1988; RPET 1995]

    A)            \[\log ({{x}^{6}}+1)+c\]

    B)            \[{{\tan }^{-1}}({{x}^{3}})+c\]

    C)            \[3{{\tan }^{-1}}({{x}^{3}})+c\]

    D)            \[3{{\tan }^{-1}}\left( \frac{{{x}^{3}}}{3} \right)+c\]

    Correct Answer: B

    Solution :

                       Put \[{{x}^{3}}=t\Rightarrow 3{{x}^{2}}dx=dt,\] therefore            \[\int_{{}}^{{}}{\frac{3{{x}^{2}}}{{{x}^{6}}+1}\,dx=\int_{{}}^{{}}{\frac{1}{{{t}^{2}}+1}dt={{\tan }^{-1}}(t)+c}}={{\tan }^{-1}}({{x}^{3}})+c\].


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