Posted by mike on Sunday, May 10, 2009 at 3:33pm.
if an is a geometric sequence where a1=4 and the sum of an=12. how would you find the common ratio of the sequence? please help

math  drwls, Sunday, May 10, 2009 at 3:49pm
You must mean the infinite sum of ALL an, up to infinity. Partial sums cannot all be the same.
Let the common ratio be x.
4(1 + x + x^2 + ...) = 12
(1 + x + x^2 + ...) = 3
Now, recognize that the infinite series adds up to 1/(1x).
1/(1x) = 3
1/x = 1/3
x = 2/3
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