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

  • question_answer
    If the roots of the equation \[12{{x}^{2}}-mx+5=0\] are in the ratio 2 : 3, then m = [RPET 2002]

    A) \[5\sqrt{10}\]

    B) \[3\sqrt{10}\]

    C) \[2\sqrt{10}\]

    D) None of these

    Correct Answer: A

    Solution :

    Let roots area, b  so, \[\frac{\alpha }{\beta }=\frac{2}{3}\Rightarrow \alpha =\frac{2\beta }{3}\] \ \[\alpha +\beta =\frac{m}{12}\] Þ \[\frac{2\beta }{3}+\beta =\frac{m}{12}\Rightarrow \frac{5\beta }{3}=\frac{m}{12}\]     ?..(i) and \[\alpha \beta =\frac{5}{12}\Rightarrow \frac{2\beta }{3}.\beta =\frac{5}{12}\,\,\Rightarrow  {{\beta }^{2}}=\frac{5}{8}\] \[\Rightarrow \beta =\sqrt{5/8}\] Put the value of b in (i), \[\frac{5}{3}.\sqrt{\frac{5}{8}}=\frac{m}{12}\]Þ \[m=5\sqrt{10}\].


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