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The sum of the first n terms in the infinite geometric sequence {1, 1/3, 1/9, 1/27, ...} is 364/243. Find n.

 Oct 9, 2020
 #1
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formula for sum of geometric series is S(n) = (a_1*(1-r^n))/1-r where r is not equal to 1. use it 

 Oct 9, 2020
 #2
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Expand the sequence:

 

1, 1/3, 1/9, 1/27, 1/81, 1/243. If you sum them up, you should get =364 / 243. Therefore, just count the number of terms, which = 6 terms.

 Oct 9, 2020

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