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Homework Help: Question regarding Binomial Theorem

  1. Dec 19, 2008 #1
    Hey people, i've racked my brain on this question for hours and can't seem to get to grips with it, wondering if i could get a little guidance?

    1. The problem statement, all variables and given/known data

    Considering the co-efficient of x^n in the expansion of (1+x)^n(1+x)^n, show:

    [the sum from k=0 -> k=n of:] [nCk]2 = 2nCn

    3. The attempt at a solution

    i've found the co-efficient of x^n by using the binomial expansion on (1+x)^2n, and i can see that the binomial expansion of (1+x)^2n will give a series of squared co-efficients, but I have no idea how to relate the two :s.

    Any help would be much appreciated.

    Cheers,
    Andrew
     
  2. jcsd
  3. Dec 19, 2008 #2
    Can't you use induction?
     
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