Question

What is the sum of an 8–term geometric series if the first term is 12 and the last term is –3,359,232?

Answer 1

(an) = (a1)r^(n - 1)
(Sn) = ( (a1)(1 - r^n) )/(1 - r)

The first formula above lets you find the common ratio, r. Plug in a8 = -3,359,232, a1 = 12, and n = 8

Once you know the common ratio, r, plug everything in to the second formula to get the sum