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

  • question_answer
    For which of the following functions, the substitution \[{{x}^{2}}=t\]is applicable   

    A)            \[\int_{{}}^{{}}{{{x}^{6}}{{\tan }^{-1}}{{x}^{3}}}\ dx\]

    B)            \[\int_{{}}^{{}}{{{\tan }^{-1}}\left( \frac{2x}{1-{{x}^{2}}} \right)\ dx}\]

    C)            \[\int_{{}}^{{}}{{{x}^{3}}\cos {{x}^{2}}\ dx}\]

    D)            None of these

    Correct Answer: C

    Solution :

                       \[{{x}^{2}}=t\] is applicable for \[\int_{{}}^{{}}{{{x}^{3}}\cos {{x}^{2}}\,dx}\]                 \[=\frac{1}{2}\int_{{}}^{{}}{t\cos t\,dt}=\frac{1}{2}(t\sin t-\int_{{}}^{{}}{\sin t\,dt+c)}\]                 \[=\frac{1}{2}(t\sin t+\cos t+c)=\frac{1}{2}({{x}^{2}}\sin {{x}^{2}}+\cos {{x}^{2}}+c).\]


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