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

  • question_answer
    If \[\alpha \] and \[\beta \] \[(\alpha <\beta )\] are the roots of the equation \[{{x}^{2}}+bx+c=0,\] where, \[c<0<b,\] then

    A) \[0<\alpha <\beta \]     

    B) \[\alpha <0<\beta <\,|\alpha |\]

    C) \[\alpha <\beta <0\]     

    D) \[\alpha <0<\,|\alpha |\,<\beta \]

    Correct Answer: B

    Solution :

    Given \[\alpha  < \beta , c < 0, b > 0,\] \[\therefore \,\,\,\alpha +\beta =-b<0 \,and \,\alpha \beta =c<0\] Clearly, \[\alpha \] and \[\beta \] have opposite signs and \[\alpha  < \beta \] \[\therefore \,\,\,\alpha  < 0 \,and \,\beta >0\,\,\,\Rightarrow \,\,\alpha <0<\beta \] Further \[\alpha +\beta <0\,\,\Rightarrow \,\,\beta <\,\,-\alpha \,\,\Rightarrow \,\,\left| \beta  \right|<\,\,\left| -\alpha  \right|\] \[\Rightarrow \,\,\,\beta <|\alpha |\,\,(\beta >0\Rightarrow \left| \beta  \right|=\beta )\] Hence, \[\alpha  < 0 < \beta  < \left| \alpha  \right| \]


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