KVPY Sample Paper KVPY Stream-SX Model Paper-9

  • question_answer
    The value of \[\int{\left[ 2\sin x \right]}\,dx\,where\left[ . \right]\]represents the greatest integer function is

    A) \[\frac{-5\pi }{3}\]                     

    B) \[-\pi \]

    C) \[\frac{5\pi }{3}\]          

    D) \[-2\pi \]

    Correct Answer: A

    Solution :

    Let \[\begin{align}   & I=\int_{\pi }^{2\pi }{\left[ 2\sin x \right]}dx \\  &  \\ \end{align}\]
    \[\pi \le x<7\pi /6\Rightarrow -1\le 2\sin x<0\]
    \[\begin{align}   & \Rightarrow \left[ 2\sin x \right]=-1 \\  & 7\pi /6\le x<11\pi /6\Rightarrow -2\le 2\sin x<-1 \\ \end{align}\]
    \[\Rightarrow \left[ 2\sin x \right]=-1\]
    \[\therefore I=\int\limits_{\pi }^{7\pi /6}{-dx+\int\limits_{7\pi /6}^{11\pi /6}{-2dx+\int\limits_{11\pi /6}^{2\pi }{-1dx}}}\]
    =\[\left( -\frac{7\pi }{6}+\pi  \right)+2\left( \frac{11\pi }{6}+\frac{7\pi }{6} \right)+\left( -2\pi +\frac{11\pi }{6} \right)\]
    =\[-\frac{\pi }{6}-\frac{8\pi }{6}-\frac{\pi }{6}=-\frac{10\pi }{6}=\frac{-5\pi }{3}\]


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