JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Self Evaluation Test - Complex Numbers and Quadratic Equations

  • question_answer
    The set of all real numbers x for which \[{{x}^{2}}-[x+2]+x>0,\] is

    A) \[\left( -\infty ,-2 \right)\cup \left( 2,\infty  \right)\]

    B) \[\left( -\infty ,-\sqrt{2} \right)\cup \left( \sqrt{2},\infty  \right)\]

    C) \[\left( -\infty ,-1 \right)\cup \left( 1,\infty  \right)\]

    D) \[\left( \sqrt{2},\infty  \right)\]

    Correct Answer: B

    Solution :

    For \[\operatorname{x}\ge -\,2,\,\,{{x}^{2}}-x-2+x>0\] \[\Rightarrow \,\,\,{{x}^{2}}>2\,\,\Rightarrow \,\,x\in (-\infty ,-\sqrt{2})\cup \,\,(\sqrt{2},\,\,\infty )\] \[\Rightarrow \,\,\,\operatorname{x}\in \left[ -\,2,-\sqrt{2} \right)\cup \left( \sqrt{2},\,\,\infty  \right) For\,\,x<-\,2\] \[{{\operatorname{x}}^{2}}+x+2+x>0 \,or\,\,{{x}^{2}}+2x+2>0\] which is true for all x. Hence \[\operatorname{x}\,\in (-\,\infty ,\,-\sqrt{2})\,\cup (\sqrt{2},\,\infty )\]


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