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Homework Help: How to prove that?

  1. Sep 16, 2006 #1
    Prove that
    [tex]\sum_{k=0}^n \binom nk 2^k = 3^n, \quad n \in \mathbb{Z}^{+}[/tex]

    Can anyone help me? Thanks
  2. jcsd
  3. Sep 16, 2006 #2


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    Homework Helper

    Do you know the binomial theorem? This is a "yes" or "no, but I looked it up in google and now I do" question.
  4. Sep 16, 2006 #3
    StatusX, thanks.
    Sorry for the stupid question! Now i work it out.
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