Question

what is the sum of an 8-term geometric series if the first term is -11, the last term is 180, 224, and the common ratio is -4​

Answer 1

The sum is
`144,177`

Explanation:

we know that

The formula of the sum in a geometric sequence is equal to

`S=a1[(1-r^(n))/(1-r)]`

where

a1 is the first term

r is the common ratio

n is the number of terms

we have

a1=-11

r=-4

n=8

substitute the values

`S=(-11)[(1-(-4)^(8))/(1-(-4))]`

`S=(-11)[(1-(65.536))/(5)]`

`S=144,177`