What is the sum of an 8th term geometric series if the first term is -11, the last term is 180,224, and the common ratio is -4

Question

asked Feb 20, 2019 133k views

1 Answer

Getter · Answer 1 · 2019-02-24T02:54:57+0000

The sum of n terms is given from the first term and the common ratio by

S_(n)=a_(1)(r^(n)-1)/(r-1)

For your given values of a1=-11, r=-4, n=8, the sum of 8 terms is

$S_(8)=(-11)((-4)^(8)-1)/(-4-1)=(-11)(65535)/(-5)\\\\=144177$