SOLUTION: Find the value for n for which the sum 1+3+9+...to n terms is 364

Question 130910: Find the value for n for which the sum 1+3+9+...to n terms is 364
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Find the value for n for which the sum 1+3+9+...to n terms is 364
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It's a geometric series with r = 3 and a(1) = 1
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S(n) = a(1)[r^(n+1) - 1]/[r - 1]
364 = 1[3^(n+1) - 1] /2
3^(n+1) -1 = 728
3^(n+1) = 729
(n+1)log3 = log729
n+1 = log729/log3
n+1 = 6
n = 5
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Cheers,
Stan H.
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