JEE Main & Advanced Sample Paper JEE Main Sample Paper-2

  • question_answer
    Let \[f'(x)=f(x)\] where \[f(0)=1\]. If \[f(x)+g(x)={{x}^{2}}\] then \[\int\limits_{0}^{1}{f(x)\cdot g(x)dx=}\]

    A)  \[\frac{{{e}^{2}}+2e-3}{2}\]                      

    B)  \[\frac{-{{e}^{2}}+2e-3}{2}\]

    C)  \[\frac{-{{e}^{2}}+2e+1}{2}\]                    

    D)  \[\frac{-{{e}^{2}}+2e-1}{2}\]

    Correct Answer: B

    Solution :

    \[y=f(x)\] \[\frac{dy}{dx}=y\] \[\Rightarrow \]               \[\frac{dy}{y}=dx\] \[\Rightarrow \]               \[y=k\cdot \,{{e}^{x}}\,\And \,f(0)=1\] \[\Rightarrow \]               \[k=1\]  \[f(x)={{e}^{x}}\] \[\Rightarrow \]               \[g(x)={{x}^{2}}-{{e}^{x}}\] \[\int\limits_{0}^{1}{{{e}^{x}}({{x}^{2}}-{{e}^{x}})dx=\left| {{x}^{2}}{{e}^{x}}-2x{{e}^{x}}+2{{e}^{x}}-\frac{{{e}^{2x}}}{2} \right|_{0}^{1}}\]\[=e-2e+2e-\frac{{{e}^{2}}}{2}-2+\frac{1}{2}=\frac{-{{e}^{2}}+2e-3}{2}\]


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