Question

What is the sum of the first 6 terms of this geometric sequence –4, –16, –64, –256?

Answer 1

The sum is `-5460`

Explanation:

The sum of a geometric progession is given by

`S=a*(1-r^n)/(1-r)` where a is the first of the progression and r is the ratio of the progession. To find it we divide two terms of the progession hence we have that

`r=-16/-4=4`

So the sum is

`S=(-4)*((4)^6-1)/(4-1)=-5460`