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    Consider the set :A={x∈Q:0<(2−1)x<2+1}A = \{ x \in \mathbb{Q} : 0 < (\sqrt{2} - 1)x < \sqrt{2} + 1 \}A={x∈Q:0<(​2\sqrt {2}2​​−1)x<​2
    Question

    Consider the set :

    A={x∈Q:0<(2−1)x<2+1}A = \{ x \in \mathbb{Q} : 0 < (\sqrt{2} - 1)x < \sqrt{2} + 1 \}A={xQ:0<(
    2\sqrt {2}2​−
    1)x<
    2\sqrt{2}2​+
    1}
    as a subset of R\mathbb{R}R. Which of the following statements is true?

    A.

    sup A = 2 + 23\sqrt{3}​​

    B.

    sup A = 3 + 22\sqrt{2}​​

    C.

    inf A = 2 + 23\sqrt{3}​​

    D.

    inf A = 3 + 22\sqrt{2}​​

    Correct option is B

    set  A consists of  elements "x" such that 

    0<(2\sqrt{2} - 1)x< (2+1\sqrt{2} +1​)

    \implies      0<x<2+1210<x<\frac{\sqrt{2}+1}{\sqrt{2}-1}

    0<x<2+1212+12+1\implies 0<x<\frac{\sqrt{2}+1}{\sqrt{2}-1}*\frac{\sqrt{2}+1}{\sqrt{2}+1}      (rationalising)

    \implies 0<x<(2+1)2(2)2120<x<\frac{(\sqrt{2}+1)^2}{(\sqrt{2})^2 - 1^2}

    0<x<2+1+2221\implies 0<x<\frac{2+1+2\sqrt{2}}{2-1}

    0<x<3+22\implies 0<x<3+2\sqrt{2}  

    hence , A = (0 , 3+22\sqrt{2} infA=0,supA=3+22\implies inf A = 0 , sup A = 3 + 2\sqrt{2} ​​

    ​​​​​

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