How to Prove Sum of Binomials Equals 3^n

steven2006 · 2006-09-16T16:07:53+00:00

Prove that \sum_{k=0}^n \binom nk 2^k = 3^n, \quad n \in \mathbb{Z}^{+} Can anyone help me? Thanks

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steven2006

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

Can anyone help me? Thanks

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StatusX

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.

steven2006

StatusX, thanks.
Sorry for the stupid question! Now i work it out.