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

  • question_answer
    If the ratio of the roots of \[a{{x}^{2}}+2bx+c=0\] is same as the ratio of the roots of \[p{{x}^{2}}+2qx+r=0\], then   [Pb. CET 1991]

    A) \[\frac{b}{ac}=\frac{q}{pr}\]

    B) \[\frac{{{b}^{2}}}{ac}=\frac{{{q}^{2}}}{pr}\]

    C) \[\frac{2b}{ac}=\frac{{{q}^{2}}}{pr}\]

    D) None of these

    Correct Answer: B

    Solution :

    If the roots of equation \[a{{x}^{2}}+2bx+c=0\]are in the ratio m : n, Then we have \[mn{{(2b)}^{2}}={{(m+n)}^{2}}ac\] .....(i) Also if the roots of the equation \[p{{x}^{2}}+2qx+r=0\]are also in the same ratio \[m:n\],  then \[mn{{(2q)}^{2}}={{(m+n)}^{2}}pr\] .....(ii) Dividing (i) and (ii), we get \[\frac{{{b}^{2}}}{{{q}^{2}}}=\frac{(ac)}{(pr)}\]or \[\frac{{{b}^{2}}}{ac}=\frac{{{q}^{2}}}{pr}\].


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