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Discussion :: Quadratic Equations

  1. If a and b are the roots of the equation x2 - 9x + 20 = 0, find the value of a2 + b2 + ab?
    2. A.
    -21
    B.
    1
    C.
    61
    D.
    21
    E.
    None of these

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    Answer : Option C

    Explanation :

    a2 + b2 + ab = a2 + b2 + 2ab - ab
    i.e., (a + b)2 - ab
    from x2 - 9x + 20 = 0, we have
    a + b = 9 and ab = 20. Hence the value of required expression (9)2 - 20 = 61.

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