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

  • question_answer
    If \[\int_{{}}^{{}}{\frac{1}{(1+x)\sqrt{x}}\ dx=f(x)+A}\], where A is any arbitrary constant, then the function \[f(x)\] is                                                                                             [MP PET 1998]

    A)            \[2{{\tan }^{-1}}x\]

    B)            \[2{{\tan }^{-1}}\sqrt{x}\]

    C)            \[2{{\cot }^{-1}}\sqrt{x}\]

    D)            \[{{\log }_{e}}(1+x)\]

    Correct Answer: B

    Solution :

               \[I=\int_{{}}^{{}}{\frac{dx}{\sqrt{x}(1+{{(\sqrt{x})}^{2}})}}\]. Put \[\sqrt{x}=t\Rightarrow \frac{1}{2\sqrt{x}}\,dx=dt\]            \[I=\int_{{}}^{{}}{\frac{2\,dt}{1+{{t}^{2}}}=2{{\tan }^{-1}}t+A}\]            \[\therefore \,\,\,I=2{{\tan }^{-1}}\sqrt{x}+A\]; \[\therefore \,\,\,f(x)=2{{\tan }^{-1}}\sqrt{x}\].


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