For finding the sum of terms in a finite geometric series, we use the following formula where = the first term in the series and
= the common ratio
(1)
(2)
Example 1:
Find the sum of the first 6 terms of the geometric series 2 + 4 + 8 + …
We’ll use the first equation knowing that ,
, and
(3)
Example 2:
Find the sum of the first n terms of the geometric series given ,
, and
(4)