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

  • question_answer
    The value of \[\int_{\pi }^{2\pi }{[2\sin x]\,dx,}\] where \[[\,\,.\,\,]\] represents the greatest integer function, is                                         [IIT 1995]

    A)                 \[-\pi \]

    B)                 \[-2\pi \]

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

    D)                 \[\frac{5\pi }{3}\]

    Correct Answer: C

    Solution :

               \[\int_{\pi }^{2\pi }{[2\sin x]dx=\int_{\pi }^{\pi +(\pi /6)}{(-1)dx+\int_{\pi +(\pi /6)}^{\pi +(\pi /2)}{\,(-2)dx}}}\]            \[+\int_{\pi +(\pi /2)}^{\pi +(\pi /2)+(\pi /3)}{\,(-2)dx+\int_{\pi +(\pi /2)+(\pi /3)}^{2\pi }{\,(-1)dx}}\]                    \[=-\frac{\pi }{6}-2\left[ \frac{\pi }{2}-\frac{\pi }{6} \right]-2\left[ \frac{\pi }{3} \right]-1\left[ \frac{\pi }{2}-\frac{\pi }{3} \right]\]                      \[=-\frac{\pi }{6}-\frac{2\pi }{3}-\frac{2\pi }{3}-\frac{\pi }{6}\]\[=-\frac{\pi }{6}-\frac{8\pi }{6}-\frac{\pi }{6}=-\frac{10\pi }{6}=-\frac{5\pi }{3}\].


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