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

Question

9415 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2018-05-17T05:11:33

$959780$

Sum of geometric sequence is $(a(r^n-1))/(r-1)$
where
a = your first number
r = the ratio
n = number of terms

In this case,

a = -4
r = $24/-4 = -144/24 = -6$
n = 8

Sum
= $(a(r^n-1))/(r-1)$

= $(-4((-6)^8-1))/(-6-1)$

= $(-4times1679615)/-7$

= $-6718460/-7$

= $959780$