text: what is the sum of the geometric series:  8 - 4 + 2 - 1 + 1/2 -...?   formula is a/(1 - r): 8/(1 - (-1/2)) = 8/(3/2) = 16/3 = 5 1/3  you can look at a few terms. the answer is  4   5   5 1/4 ...  so this answer looks pretty good.