JEE Main & Advanced Mathematics Definite Integration Question Bank Properties of Definite Integration

  • question_answer
    If \[f(x)=\int_{a}^{x}{{{t}^{3}}{{e}^{t}}\,dt\,,}\] then \[\frac{d}{dx}\,f(x)=\]         [MP PET 1989]

    A)                 \[{{e}^{x}}({{x}^{3}}+3{{x}^{2}})\]           

    B)                 \[{{x}^{3}}{{e}^{x}}\]

    C)                 \[{{a}^{3}}{{e}^{a}}\]     

    D)                 None of these

    Correct Answer: B

    Solution :

              \[f(x)=\int_{a}^{x}{{{t}^{3}}{{e}^{t}}dt=\int_{a}^{0}{{{t}^{3}}.{{e}^{t}}dt+\int_{0}^{x}{{{t}^{3}}{{e}^{t}}\,\,dt}}}\]                                 \[\Rightarrow \frac{df(x)}{dx}=\frac{d}{dx}\left( \int_{a}^{0}{{{t}^{3}}.{{e}^{t}}dt} \right)+\frac{d}{dx}\left( \int_{0}^{x}{{{t}^{3}}.{{e}^{t}}\,dt} \right)={{x}^{3}}{{e}^{x}}\].


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