JEE Main & Advanced Mathematics Indefinite Integrals Question Bank Fundamental Integration

  • question_answer
    \[\int_{{}}^{{}}{\frac{dx}{\sqrt{{{x}^{2}}-{{a}^{2}}}}}\] equals [SCRA 1996]

    A)            \[{{\sin }^{-1}}\left( \frac{x}{a} \right)+c\]

    B)            \[{{\log }_{e}}|x+\sqrt{{{x}^{2}}-{{a}^{2}}}|+c\]

    C)            \[{{\log }_{e}}|x-\sqrt{{{x}^{2}}-{{a}^{2}}}|+c\]

    D)            \[\frac{x\sqrt{{{x}^{2}}-{{a}^{2}}}}{2+c}\]

    Correct Answer: B

    Solution :

               \[I=\int_{{}}^{{}}{\frac{dx}{\sqrt{{{x}^{2}}-{{a}^{2}}}}}\]. Put\[x=a\sec \theta \Rightarrow dx=a\sec \theta \,.\,\tan \theta \,d\theta \]            \[\therefore \,\,\,I=\int_{{}}^{{}}{\frac{a\sec \theta \,.\,\tan \theta \,d\theta }{a\tan \theta }}=\int_{{}}^{{}}{\sec \theta \,d\theta }\]                   \[=\log (\sec \theta +\tan \theta )+=\log \left( \frac{x}{a}+\frac{\sqrt{{{x}^{2}}-{{a}^{2}}}}{a} \right)+c\]                   \[=\log (x+\sqrt{{{x}^{2}}-{{a}^{2}}})+c\].


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