SOLUTION: Find the sum of first 7 terms 4,12,36?

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Question 924963: Find the sum of first 7 terms 4,12,36?

Found 2 solutions by TimothyLamb, MathTherapy:
Answer by TimothyLamb(4379) About Me  (Show Source):
You can put this solution on YOUR website!
4 + 4*3 + 4*3*3 + 4*3*3*3 + 4*3*3*3*3 + 4*3*3*3*3*3 + 4*3*3*3*3*3*3 = ?
4 + 12 + 36 + 108 + 324 + 972 + 2916 = 4372
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answer:
4372
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Answer by MathTherapy(10552) About Me  (Show Source):
You can put this solution on YOUR website!
Find the sum of first 7 terms 4,12,36?

This is a geometric progression (GP) so use the formula for the sum of a G.P.:
S%5Bn%5D+=+a%5B1%5D%2A%28%281+-+r%5En%29%2F%281+-+r%29%29
n+=+7
S%5Bn%5D is the sum of the series you're seeking
a%5B1%5D+=+4
Common ratio or r+=+3