JEE Main & Advanced Mathematics Complex Numbers and Quadratic Equations Question Bank Solution of quadratic equations and Nature of roots

  • question_answer
    If the roots of the equations \[p{{x}^{2}}+2qx+r=0\]and \[q{{x}^{2}}-2\sqrt{pr}x+q=0\] be real, then

    A) \[p=q\]

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

    C) \[{{p}^{2}}=qr\]

    D) \[{{r}^{2}}=pq\]

    Correct Answer: B

    Solution :

    Equations \[p{{x}^{2}}+2qx+r=0\] and \[q{{x}^{2}}-2(\sqrt{pr})x+q=0\] have real roots, then from first \[4{{q}^{2}}-4pr\ge 0\]Þ \[{{q}^{2}}-pr\ge 0\,\,\Rightarrow {{q}^{2}}\ge pr\] .....(i) and from second \[4(pr)-4{{q}^{2}}\ge 0\](for real root ) Þ \[pr\ge {{q}^{2}}\] .....(ii) From (i) and (ii), we get result\[{{q}^{2}}=pr\].


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