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

  • question_answer
    \[\int_{{}}^{{}}{\frac{f'(x)}{{{[f(x)]}^{2}}}}\ dx=\]

    A)            \[-{{[f(x)]}^{-1}}+c\]

    B)            \[\log [f(x)]+c\]

    C)            \[{{e}^{f(x)}}+c\]

    D)            None of these

    Correct Answer: A

    Solution :

                       Put \[f(x)=t\Rightarrow {f}'(x)\,dx=dt,\] then            \[\int_{{}}^{{}}{\frac{{f}'(x)}{|f(x){{|}^{2}}}\,dx}=\int_{{}}^{{}}{\frac{1}{{{t}^{2}}}\,dt}=-\frac{1}{t}+c=-\frac{1}{f(x)}+c.\]


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