Question

What is the sum of the geometric sequence −4, 24, −144, ... if there are 8 terms?

Answer 1

Answer:

The sum of 8 geometric sequence is 959780

Step-by-step explanation:

We are given

this sequence is geometric

-4 , 24 , -144

First term is -4

so, $a_1=-4$

now, we can find common ratio

$r=\frac{24}{-4}=-6$

we can use formula

$S_n=a_1(\frac{1-r^n}{1-r} )$

n=8

now, we can plug values

$S_8=-4(\frac{1-(-6)^{8}}{1+6} )$

now, we can simplify it

and we get

$S_8=959780$