I'm a little confused on geometric series. My book says that a geometric series is a series of the type: n=1 to ∞, ∑arn-1 If r<1 the series converges to a/(1-r), otherwise the series diverges. So let's say we have a series: n=1 to ∞, ∑An, with An = 1/2n An can be re-written as (1/2)n, which apparently makes it a geometric series with r=1/2. This converges to 1/(1-1/2) = 1/(1/2) = 2. However, I was under the assumption that I was supposed to factor out a 1/2 to make the series ∑1/2(1/2)n-1. This would converge to (1/2)/(1-1/2) = (1/2)/(1/2) = 1. Why are these different? Which one is correct?