Question

What is the sum of an 8-term geometric series if the first term is -11, the last term 180,224, and the common ratio is -4? answers to choose from. can somebody please solve this?
a)-143,231
b)-36,047
c)144,177
d)716,144

Answer 1

The general formula for the sum of the n terms of a geometric progression is:

Sn = A1 (1 - r^n) / (1 - r)

In this case, n = 8; A1 = - 11, r = -4

S8 = -11 (1 - (-4)^8) / (1 -(-4)) = 144,177

Answer: option c.