JEE Main & Advanced Mathematics Equations and Inequalities Question Bank Self Evaluation Test - Linear Inequalities

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

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

    B) \[[2,\infty )\]

    C) \[[0,2)\]

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

    Correct Answer: D

    Solution :

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


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