SOLUTION: What is Sn of the geometric series with a1=3, an=-38, and n=8? A) -178 B)-102 C)-140 D) -280

SOLUTION: What is Sn of the geometric series with a1=3, an=-38, and n=8? A) -178 B)-102 C)-140 D) -280

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Question 855042: What is Sn of the geometric series with a1=3, an=-38, and n=8?
A) -178
B)-102
C)-140
D) -280

Answer by richwmiller(17219) (Show Source): You can put this solution on YOUR website!
Tn = t * r^(n - 1)
-38 = 3 * r^(7)
r = -(38/3)^(1/7)
S=t*(1 - r^n)/(1 - r)
S=3*(1 - ( -(38/3)^(1/7))^8)/(1 - ( -(38/3)^(1/7)))
arithmetic
S = �(a + an)n
S = �(3 + -38)8=-140
This is probably meant to be an arithmetic series not GEOMETRIC

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