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

  • question_answer
    \[f(x)=f(2-x),\] then \[\int_{\,0.5}^{\,1.5}{\,xf(x)\,dx}\] equals [AMU 1999]

    A)                 \[\int_{\,0}^{\,1}{\,f(x)\,dx}\]   

    B)                 \[\int_{\,0.5}^{\,1.5}{\,f(x)\,dx}\]

    C)                 \[2\int_{\,0.5}^{\,1.5}{\,f(x)\,dx}\]         

    D)                 0

    Correct Answer: B

    Solution :

               \[I=\int_{0.5}^{1.5}{xf\,(x)\,dx=\int_{0.5}^{1.5}{(2-x)f(2-x)\,dx}}\], \[\left[ \because \int_{a}^{b}{f(x)dx=\int_{a}^{b}{f(a+b-x)dx}} \right]\]                   \[=\int_{0.5}^{1.5}{(2-x)f(x)\,dx}=2\int_{0.5}^{1.5}{f(x)\,dx-I}\]Þ\[I=\int_{0.5}^{1.5}{f(x)\,dx}\].


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