Question

How do you find `S_n` for the geometric series `a_1=12`, `a_5=972`, r=-3?

Answer 1

`S_n = (12(1-(-3)^n))/4`

Explanation:

The sum to `n` of a geometric series, denoted as `S_n`, is given by the formula `S_n = (a(1-r^n))/(1-r` where `a` is the first term of the series and `r` is the common ratio.

`S_n = (12(1-(-3)^n))/(1--3 )= (12(1-(-3)^n))/4`