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

  • question_answer
    If \[f(x)\] is an odd function of \[x,\] then \[\int_{-\frac{\pi }{2}}^{\frac{\pi }{2}}{f(\cos x)\,dx}\] is equal to                                                          [MP PET 1998]

    A)                 0             

    B)                 \[\int_{0}^{\frac{\pi }{2}}{f(\cos x)\,dx}\]

    C)                 \[2\int_{0}^{\frac{\pi }{2}}{f(\sin x)\,dx}\]           

    D)                 \[\int_{0}^{\pi }{f(\cos x)\,dx}\]

    Correct Answer: C

    Solution :

               \[f(\cos x)\]is an even function.                    \[\because f(\cos (-x))=f(\cos x)\]                                 \[\therefore \,\,\int_{-\pi /2}^{\pi /2}{f(\cos x)dx=2\int_{0}^{\pi /2}{f(\cos x)dx}}\]\[=2\int_{0}^{\pi /2}{f(\sin x)dx}\].


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