Question

Find the sum of the geometric series –5, -10, -20, -40, . . . for 7 terms

Answer 1

What is the common ratio r?

Answer 2

its not listed, that is the question exactly

Answer 3

You can find it...

Answer 4

Divide the second term by the first term to get the ratio.

Answer 5

so 2?

Answer 6

-10/-5

Answer 7

2 is the common ratio

Sum of GS
\[=\frac{a(r^n-1)}{r-1}\]r=2, a=-5, n=7

Answer 8

thank you