Question

50 points!!! What is the sum of the first 8 terms of the geometric series?

Answer 1

Answer:

Sum of the 8 terms = 69.19

Step-by-step explanation:

The sum of the geometric series is S

$s=\frac{a(1-r^n)}{1-r}$

Where: a is the first term

            n is the number of terms

            r is the constant ratio.

For the giving geometric series: 120 - 80 + 160/3 - 320/9 + ...

a = 120 , n = 8

r = -80/120 = -2/3

∴ $s = \frac{120(1-(\frac{-2}{3})^8) }{1-(\frac{-2}{3}) } = \frac{50440}{729}=69\frac{139}{729}=69.19$