JEE Main & Advanced Mathematics Definite Integration Question Bank Summation of series by Definite Integration, Gamma function, Leibnitz's rule

  • question_answer
    If \[\int_{{}}^{{}}{f(x)\,dx}=x{{e}^{-\log |x|}}+f(x),\] then \[f(x)\] is        [MP PET 1997]

    A)                 1             

    B)                 0

    C)                 \[c{{e}^{x}}\]    

    D)                 \[\log x\]

    Correct Answer: C

    Solution :

                       \[\int_{{}}^{{}}{f(x)dx=x{{e}^{\log \left| \frac{1}{x} \right|}}+f(x)\Rightarrow \int_{{}}^{{}}{f(x)dx=\frac{x}{|x|}+f(x)}}\]                    On differentiating both sides , we get \[f(x)=0+f'(x)\]                                 We know \[\frac{d}{dx}({{e}^{x}})={{e}^{x}},\,\,\therefore \,\,f(x)=c{{e}^{x}}\].


You need to login to perform this action.
You will be redirected in 3 sec spinner