-1
$\begingroup$

How would I prove that $3^n = \sum_{k=0}^n \binom {n} {k} 2^k$ for any positive integer $n$?

  • 3
    Do you know the binomial theorem?2012-09-24
  • 0
    Hint: let $\:2 = x,\:$ so $\rm\:3 = 1+x.\:$ Recognize the famous theorem now?2012-09-24

3 Answers 3