I have a problem with finding the sum of this geometric series. (the characters in italics are supposed to be smaller)
a1 = 2, a6 = 486, r = 3
So, applying the sum formula:
Sn = a1 (1 - r^n) / 1 - r
Sn = 2 (1 - 3^n) / 1 - r
I don't have n to figure it out with this formula, instead I have a6, the 6th term. What am I supposed to do with that?