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

  • question_answer
    The solution set of the inequality \[\left| x+2 \right|-\left| x-1 \right|<x-\frac{3}{2}\] is

    A) \[\left( \frac{9}{2},\infty  \right)\]

    B) \[\left( -\infty ,\frac{3}{2} \right)\]

    C) \[\left( -2,-\frac{3}{2} \right)\]

    D) \[\left( -1,\frac{3}{2} \right)\]

    Correct Answer: A

    Solution :

    [a] The inequality is \[\left| x+2 \right|-\left| x-2 \right|<x-\frac{3}{2}.\]Dividing the problem into three intervals:
    (i) if \[x<-2,\] then \[-(x+2)+(x-1)<x-\frac{3}{2}\]
    \[\Rightarrow x>-\frac{3}{2}\]
    But \[-\frac{3}{2}>-2,\] hence no common values
    \[\Rightarrow x\in \phi \]
    (ii) If \[-2\le x<1,\] then \[(x+2)+(x-1)<x-\frac{3}{2}\]
    \[\Rightarrow x<-\frac{5}{2}\]
    But \[-\frac{5}{2}<-2,\] hence no common values
    \[\Rightarrow x\in \phi \]
    (iii) If \[x\ge 1,\]then \[(x+2)-(x-1)<x-\frac{3}{2}\]
    \[\Rightarrow x>\frac{9}{2}\]
    \[\because \frac{9}{2}>1.\]
    \[\Rightarrow \] common solution is
    \[x>\frac{9}{2}\Rightarrow x\in \left( \frac{9}{2},\infty  \right)\]
    \[\therefore \] Solution set is \[x\in \left( \frac{9}{2},\infty  \right)\]


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