KVPY Sample Paper KVPY Stream-SX Model Paper-17

  • question_answer
    For \[x\in \mathbf{R},\left| \left| x \right| \right|\] is defined as follows: \[\left\| x \right\|=\left\{ \begin{align}   & x+1,0\le x<2 \\  & \left| x-4 \right|,x\ge 2 \\ \end{align} \right.\] Then the solution set of the equation \[{{\left\| x \right\|}^{2}}+x=\left\| x \right\|+{{x}^{2}}\]is

    A) \[\{-1,1\}\]

    B) \[\left[ 2,\infty  \right)\]

    C) \[\left[ 0,2 \right)\]

    D) \[\{0,2\}\]

    Correct Answer: D

    Solution :

    Case1: Let \[0\le x<2\], then \[\left\| x \right\|=x+1\]and the equation becomes
    \[{{(x+1)}^{2}}+x=(x+1)+{{x}^{2}}\Rightarrow 2x=0\]
    \[\Rightarrow 2x=0\Rightarrow x=0\]
    Case 2: Let \[x\ge 2\], then \[\left\| x \right\|=\left| x-4 \right|\]and the equation becomes \[{{\left| x-4 \right|}^{2}}+x=\left| x-4 \right|+{{x}^{2}}\]
    \[\Rightarrow \]\[{{x}^{2}}-8x+16+x=\left| x-4 \right|+{{x}^{2}}\]\[\Rightarrow \]\[\left| x-4 \right|=16-17x\]
    \[\therefore \]\[x-4=\pm (16-7x)\], provided \[16-7x\ge 0\]
    \[\therefore \]\[x=\frac{5}{2}\]or 2, but for\[x=\frac{5}{2},16-7x\ge 0,\]
    Hence rejected
    \[\therefore \]\[x=2.\]
    The solution set is\[\,\{0,2\}\].


You need to login to perform this action.
You will be redirected in 3 sec spinner