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

  • question_answer
    If the sum of the roots of the equation \[{{x}^{2}}+px+q=0\] is equal to the sum of their squares, then [Pb. CET 1999]

    A) \[{{p}^{2}}-{{q}^{2}}=0\]

    B) \[{{p}^{2}}+{{q}^{2}}=2q\]

    C) \[{{p}^{2}}+p=2q\]

    D) None of these

    Correct Answer: C

    Solution :

    Let the roots be a and b  Þ \[\alpha +\beta =-p\], \[\alpha \beta =q\] Given, \[\alpha +\beta ={{\alpha }^{2}}+{{\beta }^{2}}\] But \[\alpha +\beta ={{(\alpha +\beta )}^{2}}-2\alpha \beta \] \[\Rightarrow -p={{(-p)}^{2}}-2q\] \[\Rightarrow {{p}^{2}}-2q=-p\] \[\Rightarrow {{p}^{2}}+p=2q\].


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