JEE Main & Advanced JEE Main Paper (Held On 10-Jan-2019 Evening)

  • question_answer
    The value of \[\int\limits_{-\pi /2}^{\pi /2}{\frac{dx}{[x]+[sin\,x]+4}}\] where [t] denotes the greatest integer less than or equal to t, is- [JEE Main Online Paper (Held On 10-Jan-2019 Evening]

    A) \[\frac{1}{12}(7\pi -5)\]                          

    B) \[\frac{1}{12}(7\pi +5)\]

    C) \[\frac{3}{10}(4\pi -3)\]  

    D)                  \[\frac{3}{20}(4\pi -3)\]

    Correct Answer: D

    Solution :

    \[\int\limits_{-\pi /2}^{-1}{\frac{dx}{2-1}+\int\limits_{-1}^{0}{\frac{dx}{3-1}}+\int\limits_{0}^{1}{\frac{dx}{4}}+\int\limits_{1}^{\pi /2}{\frac{dx}{5+0}}}\] \[=\,\,\,{{(x)}^{-1}}_{-\pi /2}+\frac{1}{2}{{(x)}^{0}}_{-1}+\frac{1}{4}{{(x)}^{1}}_{0}+\frac{1}{5}{{(x)}_{1}}^{\pi /2}\] \[=\,\,\left( -1+\frac{\pi }{2} \right)+\frac{1}{2}(1)+\frac{1}{4}+\frac{1}{5}\left( \frac{\pi }{2}-1 \right)\] \[=\,\,-1+\frac{\pi }{2}+\frac{1}{2}+\frac{1}{4}+\frac{\pi }{10}-\frac{1}{5}\] \[=\,\,-\frac{1}{2}+\frac{1}{4}-\frac{1}{5}+\frac{\pi }{2}+\frac{\pi }{10}\] \[=\,\,\,\frac{-10+5-4}{20}+\frac{5\pi +\pi }{10}\] \[=\,\,-\frac{9}{20}+\frac{6\pi }{10}=-\frac{9}{20}+\frac{3\pi }{5}=\frac{3}{20}(4\pi -3)\]


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