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Homework Help: Proof of Lagrange's Identity

  1. Apr 9, 2009 #1
    1. The problem statement, all variables and given/known data
    Prove Lagrange's identity for real numbers


    3. The attempt at a solution

    I tried one of the methods used in proving the Cauchy-Schwarz inequality (Ax^2 + Bx + C is greater than or equal to zero, where a = the sum from k=1 to n of (ak)^2, b = the sum from k=1 to n of (ak*bk), and c = the sum from k=1 to n of (bk)^2), but I couldn't get very far because I don't understand the last term of the equation's right side. Anyone have any ideas on how to start the problem? Thanks.
  2. jcsd
  3. Apr 9, 2009 #2
    All that was given in the textbook was a proof of the cauchy-schwarz inequality. The binet-cauchy identity, which was used in some of the proofs I glanced at, was never mentioned.
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