Question

What is the sum of the geometric sequence -3, 18, -108, ... if there are 8 terms

Answer 1

Explanation:

common ratio=18/-3=-108/18=-6, a=-3

sn=a(r^n-1)(r-1)

sn=-3((-6)^n-1)(-6-1)

sn=-3(-6)^8-1)/(-7)

s8=-3(1679615)/(-7)

s8=719836