Question

Use the formula Sn to find the sum of the first five terms of the geometric sequence.

Answer 1

First, find the common ratio r:

-4/9 : 4/3 = -1/3

4/3 : -4 = -1/3

-4:12 = -1/3

r= -1/3

`Sn=(a(r^n-1))/(r-1)`

Where:

a= first term = 12

n= number of terms = 5

Replacing:

`Sn=\frac{12(-\frac{1^{}}{3}^5-1)}{-(1)/(3)-1}`

Sn= 244/27 = 9 1/27