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

  • question_answer
    The quadratic equation whose one root is \[\frac{1}{2+\sqrt{5}}\] will be  [RPET 1987]

    A) \[{{x}^{2}}+4x-1=0\]

    B) \[{{x}^{2}}+4x+1=0\]

    C) \[{{x}^{2}}-4x-1=0\]

    D) \[\sqrt{2}{{x}^{2}}-4x+1=0\]

    Correct Answer: A

    Solution :

    Let \[\alpha =\frac{1}{2+\sqrt{5}}\]and \[\beta =\frac{1}{2-\sqrt{5}}\] Sum of roots \[\alpha +\beta =-4\]and product of roots \[\alpha \beta =-1\] Thus required equation is \[{{x}^{2}}+4x-1=0\]


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