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

  • question_answer
    \[\int_{{}}^{{}}{\frac{x}{1+{{x}^{4}}}\ dx=}\]      [IIT 1978; UPSEAT 2002]

    A)            \[\frac{1}{2}{{\cot }^{-1}}{{x}^{2}}+c\]

    B)            \[\frac{1}{2}{{\tan }^{-1}}{{x}^{2}}+c\]

    C)            \[{{\cot }^{-1}}{{x}^{2}}+c\]

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

    Correct Answer: B

    Solution :

                       Put \[t={{x}^{2}}\Rightarrow dt=2x\,dx,\] therefore            \[\int_{{}}^{{}}{\frac{x}{1+{{x}^{4}}}\,dx=\frac{1}{2}\int_{{}}^{{}}{\frac{1}{1+{{t}^{2}}}\,dt=\frac{1}{2}{{\tan }^{-1}}t+c=\frac{1}{2}{{\tan }^{-1}}{{x}^{2}}+c}}\].


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