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

Answer:

The sum is $144,177$

Step-by-step explanation:

we know that

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

$S=a1[\frac{1-r^{n}}{1-r}]$

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

$S=(-11)[\frac{1-(-4)^{8}}{1-(-4)}]$

$S=(-11)[\frac{1-(65.536)}{5}]$

$S=144,177$