JEE Main & Advanced Sample Paper JEE Main - Mock Test - 45

  • question_answer
    If [x] denotes the greatest integer \[\le x\], then the value of \[\int\limits_{4}^{10}{\frac{[{{x}^{2}}]}{[{{x}^{2}}-28x+196]+[{{x}^{2}}]}dx}\] is-

    A) 3          

    B)        2

    C) 1                     

    D)        0

    Correct Answer: A

    Solution :

       [a] We have \[I=\int\limits_{4}^{10}{\frac{[{{x}^{2}}]dx}{[(14-{{x}^{2}})]+[{{x}^{2}}]dx}}\] by using property \[\int\limits_{a}^{b}{f(x)dx}=\int\limits_{a}^{b}{f(a+b-x)dx}\] Also, \[I=\int\limits_{4}^{10}{\frac{[(4+10-{{x}^{2}})dx]}{[{{(14-(14-x))}^{2}}]+[{{(14-x)}^{2}}]}}\] \[2I=\int\limits_{4}^{10}{\left( \frac{[{{x}^{2}}]}{[{{(14-x)}^{2}}]+{{[x]}^{2}}}+\frac{[{{(14-x)}^{2}}]}{{{[x]}^{2}}+[{{(14-x)}^{2}}]} \right)dx}\] \[=\int\limits_{4}^{10}{1.dx\Rightarrow I=3}\]              


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