Asked by felix

evaluate each geometric series described
21) -3 + 15 - 75 + 375..., n=6
22) 1 + 5 + 25 + 125..., n=8
Answered by oobleck
r = -5
r = 5
You can tell what a is, and now

Sn = a(r^n - 1)/(r-1)
so just plug in your numbers