Question

What is the sum of the geometric sequence 8, -16, 32 . if there are 15 terms?

Answer 1

a=8
r=-16/8=-2
n=15
\[S _{n}=\frac{ a \left( r^n-1 \right) }{ r-1 }\]

Answer 2

Thanks so much~

Answer 3

yw