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

  • question_answer
    The real roots of the equation \[{{x}^{2}}+5|x|+4=0\] are

    A) \[\{-1,-4\}\]        

    B) \[\{1,4\}\]

    C) \[\{-4,4\}\]         

    D) None of these

    Correct Answer: D

    Solution :

    Case 1: \[\operatorname{x} \ge  0\] \[\therefore  the \,equation \,becomes \,{{x}^{2}}+5x+4=0\] or \[\operatorname{x}=-1,\,\,-4\,\,but\, x\ge 0\] \[\therefore \] both values, non-admissible: Case 2: \[\operatorname{x} \le  0\] The eqn becomes \[{{\operatorname{x}}^{2}}- 5x + 4 = 0 \,or \,\,x = 1,\,\,\,4\] both values are non-admissible, \[\therefore \] No real roots. Alternatively, since \[{{\operatorname{x}}^{2}} \ge  0; \,\,\left| \,x\, \right| \ge  0\] \[\therefore  \,{{x}^{2}} + \left| \,x\, \right| + 4 > 0 \,for \,all \,x \in  R\] \[\therefore  \,{{x}^{2}} + \left| \,x\, \right| + 4 \ne  0 \,for \,all \,x \in  R\]


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