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

  • question_answer
    \[\int_{{}}^{{}}{\frac{{{x}^{3}}}{\sqrt{1-{{x}^{8}}}}dx=}\]

    A)            \[\frac{1}{2}{{\sin }^{-1}}({{x}^{4}})+c\]

    B)            \[\frac{1}{3}{{\sin }^{-1}}({{x}^{4}})+c\]

    C)            \[\frac{1}{4}{{\sin }^{-1}}({{x}^{4}})+c\]

    D)            None of these

    Correct Answer: C

    Solution :

                       \[\int_{{}}^{{}}{\frac{{{x}^{3}}}{\sqrt{1-{{x}^{8}}}}\,dx=\int_{{}}^{{}}{\frac{{{x}^{3}}}{\sqrt{1-{{({{x}^{4}})}^{2}}}}}}\]            Put \[{{x}^{4}}=t\Rightarrow 4{{x}^{3}}dx=dt,\] then it reduces to            \[\frac{1}{4}\int_{{}}^{{}}{\frac{dt}{\sqrt{1-{{x}^{2}}}}=\frac{1}{4}[{{\sin }^{-1}}(t)]+c=\frac{1}{4}{{\sin }^{-1}}({{x}^{4}})+c.}\]


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