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

  • question_answer
    The value of \[\int_{{}}^{{}}{\frac{dx}{\sqrt{x}\,(x+9)}dx}\] is equal to    [Pb. CET 2002]

    A)            \[{{\tan }^{-1}}\sqrt{x}\]

    B)            \[{{\tan }^{-1}}\left( \frac{\sqrt{x}}{3} \right)\]

    C)            \[\frac{2}{3}{{\tan }^{-1}}\sqrt{x}\]

    D)            \[\frac{2}{3}{{\tan }^{-1}}\left( \frac{\sqrt{x}}{3} \right)\]

    Correct Answer: D

    Solution :

                       We have, \[I=\int_{{}}^{{}}{\frac{dx}{\sqrt{x}(x+9)}}\]            Put \[\sqrt{x}=t\], squaring both sides, we get \[x={{t}^{2}}\] and \[dx=2tdt\]            \[\therefore \]\[I=2\int_{{}}^{{}}{\frac{dt}{{{t}^{2}}+{{3}^{2}}}}=\frac{2}{3}{{\tan }^{-1}}\left( \frac{t}{3} \right)\] Þ \[I=\frac{2}{3}{{\tan }^{-1}}\left( \frac{\sqrt{x}}{3} \right)\].


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