JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Relation between roots and coefficients

  • question_answer
    If the roots of the equation \[a{{x}^{2}}+bx+c=0\] are \[\alpha ,\beta \], then the value of \[\alpha {{\beta }^{2}}+{{\alpha }^{2}}\beta +\alpha \beta \] will be [EAMCET 1980; AMU 1984]

    A) \[\frac{c(a-b)}{{{a}^{2}}}\]

    B) 0

    C) \[-\frac{bc}{{{a}^{2}}}\]

    D) None of these

    Correct Answer: A

    Solution :

    \[\alpha +\beta =-\frac{b}{a}\]and\[\alpha \beta =\frac{c}{a}\] Now \[\alpha {{\beta }^{2}}+{{\alpha }^{2}}\beta +\alpha \beta =\alpha \beta (\beta +\alpha )+\alpha \beta \] \[=\alpha \beta (1+\alpha +\beta )=\frac{c}{a}\left\{ 1+\left( -\frac{b}{a} \right) \right\}=\frac{c(a-b)}{{{a}^{2}}}\]


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