SOLUTION: im suppose to find the sum of the geometric series for 3 -6+12-....to 7 terms and im not quite sure how 2 do that

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Question 232039: im suppose to find the sum of the geometric series for 3 -6+12-....to 7 terms and im not quite sure how 2 do that
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
I am supposed to find the sum of the geometric series
for 3 -6+12-....to 7 terms
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Sum Formula: S(n) = a[(r^(n)-1]/[r-1]
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Your Problem:
a = 3
r = -6/3 = -2
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S(7) = 3[(-2)^7-1]/[-2-1]
S(7) = 3[-128-1]/[-3]
S(7) = 3[-129]/-3
S(7) = 129
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Cheers,
Stan H.