Starting with the 2nd term divide each term by the preceding term:
15/5 = 3
45/15 = 3
135/45 = 3
405/135 = 3
Since they are all the same, that shows that it is a geometric series
with first term a1 = 5, common ratio r = 3, and number of terms n = 14.
The formula for the sum Sn of a geometric series with first
term a1, common ratio r, and number of terms n is:
Plugging in a1 = 5, r = 3, and n = 14 into the formula:
You simplify that. The answer is an 8-digit number
Edwin
