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

  • question_answer
    \[\int{{{\cos }^{-1}}\left( \frac{1}{x} \right)\,\,dx}\]         [RPET 2002]

    A)                 \[x{{\sec }^{-1}}x+{{\cosh }^{-1}}x+C\]

    B)                 \[x{{\sec }^{-1}}x-{{\cosh }^{-1}}x+C\]

    C)                 \[x{{\sec }^{-1}}x-{{\sin }^{-1}}x+C\]

    D)                 None of these

    Correct Answer: B

    Solution :

                    \[I=\int{{{\cos }^{-1}}\left( \frac{1}{x} \right)\,dx}\]\[=\int{{{\sec }^{-1}}x.1\,\,dx}\]                   \[={{\sec }^{-1}}x\int{dx-\int{\left[ \frac{d}{dx}{{\sec }^{-1}}x\int{dx\,} \right]}\,dx}\]                   \[=x{{\sec }^{-1}}x-\int{\frac{1}{x\sqrt{{{x}^{2}}-1}}x.\,\,dx}\]                   \[=x{{\sec }^{-1}}x-\int{\frac{1}{\sqrt{{{x}^{2}}-1}}dx}\]\[=x{{\sec }^{-1}}x-{{\cosh }^{-1}}x+c\].


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