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Need help finding a bound for an equation

  1. Jul 12, 2012 #1
    I'm trying to find a value K>o such that for real a,b,c,d

    (a^2+c^2)x^2+2(ab+cd)xy+(b^2+d^2)y^2 ≤ K(x^2+y^2).

    Any help on this would be greatly appreciated thanks.
  2. jcsd
  3. Jul 12, 2012 #2


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    Well, play a bit around using the fact that 2xy is always less than the sum of the two variables squared.
  4. Jul 12, 2012 #3
    Thank you very much. I would have been stuck for hours.
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