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

  • question_answer
    The value of \[\int_{{}}^{{}}{\frac{dx}{x\sqrt{{{x}^{4}}-1}}}\] is

    A)            \[\frac{1}{2}{{\sec }^{-1}}{{x}^{2}}+k\]

    B)            \[\log x\sqrt{{{x}^{4}}-1}+k\]

    C)            \[x\log \sqrt{{{x}^{4}}-1}+k\]

    D)            \[\log \sqrt{{{x}^{4}}-1}+k\]

    Correct Answer: A

    Solution :

                       \[I=\int_{{}}^{{}}{\frac{dx}{x\sqrt{{{x}^{4}}-1}}}\]            Put \[{{x}^{2}}=t\Rightarrow 2x\,dx=dt\Rightarrow dx=\frac{dt}{2x}=\frac{dt}{2\sqrt{t}}\]            \[\therefore \,\,\,I=\int_{{}}^{{}}{\frac{dt}{2t\sqrt{{{t}^{2}}-1}}}=\frac{1}{2}{{\sec }^{-1}}t+k=\frac{1}{2}{{\sec }^{-1}}{{x}^{2}}+k\]


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