Question

What is the sum of an 8–term geometric series if the first term is –11, the last term is 859,375, and the common ratio is –5?


–143,231

716,144

144,177

–36,047

Answer 1

716,144?

Answer 2

I got -716144

Answer 3

what formula you used? \[S=a\frac{1-r^n}{1-r}\]
this?

Answer 4

No it looks like:
a1 - a1 (r)^n
Sn = _______________
1 - r

Answer 5

it's same

Answer 6

a1-a1r^n=a1(1-r^n)

Answer 7

i calculated wrongly, you are correct, sorry

Answer 8

Haha it's ok, thank you

Answer 9

i calculated as
\[S=a\frac{r^n-1}{1-r}\]
mixed r^n and 1 ><

Answer 10

Ty!!! This was correct!