Question 988822: Find the sum of the geometric sequence –3, 15, –75, 375, … when there are 7 terms
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! Find the sum of the geometric sequence –3, 15, –75, 375, … when there are 7 terms
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a(1) = -3
r = 15/(-3) = -5
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Sum = (-3)[(-5)^7 -1)/(-3-1)] = -3[(-78125 -1)/(-4)] = (3/4)(-78126) = -58594.5
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Cheers,
Stan H.
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