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

  • question_answer
    If \[I=\int_{0}^{100\pi }{\sqrt{(1-\cos 2x)}\,dx,}\]then the value of \[I\] is

    A)                 \[100\sqrt{2}\] 

    B)                 \[200\sqrt{2}\]

    C)                 \[50\sqrt{2}\]   

    D)                 None of these

    Correct Answer: B

    Solution :

               \[I=\int_{0}^{\pi }{\sqrt{(1-\cos 2x)}dx+\int_{\pi }^{2\pi }{\sqrt{(1-\cos 2x)}}dx}+....\]             \[.....+\int_{(r-1)\pi }^{r\pi }{\sqrt{(1-\cos 2x)}dx+.....+\int_{99\pi }^{100\pi }{\sqrt{(1-\cos 2x)}}dx}\]                    \[\because \int_{0}^{na}{f(x)dx=n\int_{0}^{a}{f(x)dx}}\], if \[f(a+x)=f(x)\]                    \[\therefore \]\[I=100\int_{0}^{\pi }{\sqrt{(1-\cos 2x)}}dx\]                       \[I=100\sqrt{2}\int_{0}^{\pi }{\sin xdx=200\sqrt{2}\int_{0}^{\pi /2}{\,\sin x\,dx}}\]                                       \[=200\sqrt{2}[-\cos x]_{0}^{\pi /2}=200\sqrt{2}\].


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