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

  • question_answer
    If \[f(x)=\int_{{{x}^{2}}}^{{{x}^{4}}}{\sin \sqrt{t}\,dt,}\] then \[{f}'(x)\] equals

    A)                 \[\sin {{x}^{2}}-\sin x\] 

    B)                 \[4{{x}^{3}}\sin {{x}^{2}}-2x\sin x\]

    C)                 \[{{x}^{4}}\sin {{x}^{2}}-x\sin x\]             

    D)                 None of these

    Correct Answer: B

    Solution :

                       We have \[f(x)=\int_{{{x}^{2}}}^{{{x}^{4}}}{\sin \sqrt{t}}\,dt\]                    \\[f'(x)=\frac{d}{dx}({{x}^{4}})(\sin \sqrt{{{x}^{4}}})-\frac{d}{dx}({{x}^{2}})\,(\sin \sqrt{{{x}^{2}}})\]                                    \[=4{{x}^{3}}\sin {{x}^{2}}-2x\sin x\].


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