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

  • question_answer
    \[\int_{{}}^{{}}{\frac{{{a}^{x}}}{\sqrt{1-{{a}^{2x}}}}dx=}\] [MNR 1983, 87]

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

    B)            \[{{\sin }^{-1}}{{a}^{x}}+c\]

    C)            \[\frac{1}{\log a}{{\cos }^{-1}}{{a}^{x}}+c\]

    D)            \[{{\cos }^{-1}}{{a}^{x}}+c\]

    Correct Answer: A

    Solution :

                       Put \[{{a}^{x}}=t\Rightarrow {{a}^{x}}{{\log }_{e}}a\,dx=dt,\] then            \[\int_{{}}^{{}}{\frac{{{a}^{x}}}{\sqrt{1-{{a}^{2x}}}}\,dx=\frac{1}{{{\log }_{e}}a}\int_{{}}^{{}}{\frac{dt}{\sqrt{1-{{t}^{2}}}}}}\]                               \[=\frac{1}{{{\log }_{e}}a}{{\sin }^{-1}}(t)+c=\frac{{{\sin }^{-1}}({{a}^{x}})}{{{\log }_{e}}a}+c\].


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