JEE Main & Advanced Sample Paper JEE Main Sample Paper-42

  • question_answer
    For   any   integer   n   the   integral \[\int_{0}^{\pi }{{{e}^{{{\cos }^{2}}x}}}{{\cos }^{3}}(2n+1)xdx\]has the value

    A) \[\pi \]                          

    B)  1

    C)  0                                

    D)  None of these

    Correct Answer: D

    Solution :

    Let\[I=\int_{0}^{\pi }{{{e}^{{{\cos }^{2}}x}}}.{{\cos }^{3}}(2n+1)xdx\]Using \[\int_{0}^{a}{f(x)dx}\left\{ \begin{align}   & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,0,f(a-x)=-f(x) \\  & 2\int_{0}^{a/2}{f(x)dx,f(a-x)=f(x)} \\ \end{align} \right.\] where,  \[f(x)={{e}^{{{\cos }^{2}}x}}.{{\cos }^{3}}(2n+1)x\] Now, \[f(\pi -x)=({{e}^{{{\cos }^{2}}x}})[-{{\cos }^{3}}(2n+1)x]\] \[=-f(x)\] \[\therefore \]\[I=0\]


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