JEE Main & Advanced JEE Main Paper (Held On 19 May 2012)

  • question_answer
    Let\[p,q,r\in R\]and \[r>p>0.\]If the quadratic equation\[p{{x}^{2}}+qx+r=0\] has two complex roots \[\alpha \]and \[\beta ,\]then\[|\alpha |+|\beta |\]is.       JEE Main  Online Paper (Held On 19  May  2012)

    A) equal to 1

    B)                        less than 2 but not equal to 1

    C)                        greater than 2  

    D)                        equal to 2

    Correct Answer: C

    Solution :

                    Given quadratic equation is \[p{{x}^{2}}+qx+r=0\]                                    ?(1) \[D={{q}^{2}}-4pr\] Since \[\alpha \] and \[\beta \] are two complex root \[\therefore \]\[\beta =\overline{\alpha }\Rightarrow |\beta |=|\overline{\alpha }|\Rightarrow |\beta |=|\alpha |\]\[(\because |\overline{\alpha }|=||\alpha |)\] Consider \[|\alpha |+|\beta |=|\alpha |+|\alpha |\]        \[(\because |\beta |=|\alpha |)\] \[=2|\alpha |>2.1=2\]   \[(\because |\alpha |>1)\] Hence,\[|\alpha |+|\beta |\]is greater than 2.


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