Answer:
-425
Step-by-step explanation:
You want the sum of the first 8 terms of the geometric series with first term 5 and common ratio -2.
Series sum
The sum is given by the formula ...
Sn = a1·(r^n -1)/(r -1) . . . . . . a1 = first term, r = common ratio
The sum of 8 terms of the given series is ...
S8 = 5·((-2)^8 -1)/(-2 -1) = 5(255/-3) = -1275/3 = -425
The sum of 8 terms is -425.
