Ok so I should know how to do this but I am stuck. What do you do for this one when n=2? I was thinking about making a geometric series but if you make n=1 then it becomes $ 4^{n+1} $ in the denominator and I don't know what to do with that.
--Klosekam 14:21, 30 October 2008 (UTC)
I don't have my work right in front of me, but when you have a geometric sequence that doesn't start at n = 1, or a power that isn't (n-1), you can fake it by rewriting the sum as you desire and then subtract out the terms that would be omitted in the original equation. It helps to write out the first few terms for each sum to see which need to be eliminated. --John Mason
