SOLUTION: In a geometric series, t1=3 and s3=21. Find the common ratio and the sum of the first 7 terms.
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Question 758581: In a geometric series, t1=3 and s3=21. Find the common ratio and the sum of the first 7 terms.
Answer by reviewermath(1029) (Show Source): You can put this solution on YOUR website!
Q:
In a geometric series, = 3 and = 21. Find the common ratio and the sum of the first 7 terms.
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A:
3 + 3r + = 21
1 + r + = 7
+ r - 6 = 0
(r + 3)(r - 2) = 0
r = 2 OR -3
The common ratio, r is or .
If the common ratio is 2, then the sum of the first 7 terms is:
3 + 6 + 12 + 24 + 48 + 96 + 192 = .
If the common ratio is -3, then the sum of the first 7 terms is:
3 + (-9) + 27 + (-81) + 243 + (-729) + 2187 =
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