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

  • question_answer
    If \[\alpha ,\beta \] be the roots of the equation \[{{x}^{2}}-2x+3=0\], then the equation whose roots are \[\frac{1}{{{\alpha }^{2}}}\]and \[\frac{1}{{{\beta }^{2}}}\] is

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

    B) \[9{{x}^{2}}+2x+1=0\]

    C) \[9{{x}^{2}}-2x+1=0\]

    D)         \[9{{x}^{2}}+2x-1=0\]

    Correct Answer: B

    Solution :

    \[\alpha ,\beta \] be the roots of \[{{x}^{2}}-2x+3=0\],  then \[\alpha +\beta =2\] and \[\alpha \beta =3\]. Now required equation whose roots are  \[\frac{1}{{{\alpha }^{2}}},\frac{1}{{{\beta }^{2}}}\]is \[{{x}^{2}}-\left( \frac{1}{{{\alpha }^{2}}}+\frac{1}{{{\beta }^{2}}} \right)x+\frac{1}{{{\alpha }^{2}}{{\beta }^{2}}}=0\] Þ \[{{x}^{2}}-\left( -\frac{2}{9} \right)x+\frac{1}{9}=0\]Þ \[9{{x}^{2}}+2x+1=0\].


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