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Quadratic Equation

  1. Jan 18, 2013 #1
    1. The problem statement, all variables and given/known data

    If the roots of x^2 - 2x + 4 = 0 are x1 and x2, what is x1^2 + x2^2?

    2. Relevant equations

    3. The attempt at a solution

    I don't think these questions can be answered by solving for x only cause there will be no real root(complex number).

    So I found that x1 + x2 = 2 and x1 * x2 = 4 via Vieta's theorem.
    And I tried solving it with the quadratic formula but as I said it hasn't got a real root.
  2. jcsd
  3. Jan 18, 2013 #2


    Staff: Mentor

    That's a good start.

    x12 + x22 = (x1 + x2)2 - 2x1x2, right?
  4. Jan 18, 2013 #3
    How did you get to that equation? :O
  5. Jan 18, 2013 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Expand (x1 + x2)2 & see what you get.
  6. Jan 18, 2013 #5
    Oh, right.. Thanks!
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