JEE Main & Advanced Mathematics Definite Integration Question Bank Fundamental definite integration, Definite integration by substitution

  • question_answer
    \[\int_{0}^{\pi /6}{(2+3{{x}^{2}})\cos 3x\,dx=}\]                                               [DSSE 1985]

    A)                 \[\frac{1}{36}(\pi +16)\]               

    B)                 \[\frac{1}{36}(\pi -16)\]

    C)                 \[\frac{1}{36}({{\pi }^{2}}-16)\] 

    D)                 \[\frac{1}{36}({{\pi }^{2}}+16)\]

    Correct Answer: D

    Solution :

               Let \[I=\int_{0}^{\pi /6}{\left( 2+3{{x}^{2}} \right)\cos 3x\,dx}\]                            \[=\left[ \frac{\sin 3x}{3}(2+3{{x}^{2}}) \right]_{0}^{\pi /6}-\int_{0}^{\pi /6}{\frac{\sin 3x}{3}}.6x.dx\]                                         \[=\frac{1}{36}({{\pi }^{2}}+16)\].


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