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

  • question_answer
    If the roots of the equation \[{{x}^{2}}+x+1=0\] are \[\alpha ,\beta \] and the roots of the equation \[{{x}^{2}}+px+q=0\] are \[\frac{\alpha }{\beta },\frac{\beta }{\alpha }\] then \[p\] is equal to [RPET 1987]

    A) -2

    B) -1

    C) 1

    D) 2

    Correct Answer: C

    Solution :

    Given that \[\alpha \]and \[\beta \]be the roots of \[{{x}^{2}}+x+1=0\], so \[\alpha +\beta =-1\]and \[\alpha \beta =1\] Again \[\frac{\alpha }{\beta }\]and \[\frac{\beta }{\alpha }\]are the roots of \[{{x}^{2}}+px+q=0,\] so \[\frac{\alpha }{\beta }+\frac{\beta }{\alpha }=-p\] Þ \[-p=\frac{{{\alpha }^{2}}+{{\beta }^{2}}}{\alpha \beta }\] Þ  \[-p=\frac{{{(\alpha +\beta )}^{2}}-2\alpha \beta }{\alpha \beta }=\frac{1-2}{1}\Rightarrow p=1\]


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