JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Condition for common roots, Quadratic expressions and Position of roots

  • question_answer
    If a and b (a < b) are the roots of the equation \[{{x}^{2}}+bx+c=0,\] where \[c<0<b,\] then [IIT Screening 2000; Pb. CET 2000]

    A) \[0<\alpha <\beta \]

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

    C) \[\alpha <\beta <0\]

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

    Correct Answer: B

    Solution :

    Here \[D={{b}^{2}}-4c>0\] because c < 0 < b. So roots are real and unequal. Now, \[\alpha +\beta =-b<0\] and \[\alpha \beta =c<0\] \ One root is positive and the other negative, the negative root being numerically bigger. As \[\alpha <\beta ,\,\alpha \]is the negative root while b is the positive root. So, \[|\alpha |\,>\beta \,\text{and}\,\,\alpha <0<\beta .\]  


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