JEE Main & Advanced Sample Paper JEE Main Sample Paper-18

  • question_answer
    Let \[f(x)=\frac{{{x}^{2}}+2}{[x]},\]\[1\le x\le 3\] (where [.] greatest integer function). Then least value of\[f(x)\]is

    A)  2                                            

    B)  3

    C)  3/2                       

    D)  1

    Correct Answer: B

    Solution :

     \[f(x)=\left\{ \begin{align}   & {{x}^{2}}+2,\,\,1\le x<2 \\  & \frac{{{x}^{2}}+2}{2},\,\,2\le x<3 \\  & \frac{{{x}^{2}}+2}{3},\,\,x=3 \\ \end{align} \right.\] \[f'(x)=\left\{ \begin{align}   & 2x,\,1<x<2 \\  & x,\,2<x<3 \\ \end{align} \right.\] Thus, least value of\[f(x)\]in [1, 2] is 3 and least value of\[f(x)\]in [2, 3] is 3. \[f(3)=\frac{11}{3}\] Thus, least value of\[f(x)\]is 3.


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