4+12+36+...;n=15

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4+12+36+...;n=15

Guest May 8, 2014

+8

Best Answer

$\text{The sum is }2*\left(3^n-1 \right)$

$\text{If n=15 the sum is }2*(3^{15}-1)=28697812$

Guest May 8, 2014

Guest · Answer 1 · 2014-05-08T03:11:47

$\text{The sum is }2*\left(3^n-1 \right)$

$\text{If n=15 the sum is }2*(3^{15}-1)=28697812$

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CPhill · Answer 2 · 2014-05-08T02:54:55

I believe you have a geometric series here, and you would like to find the 15th term ??

The terms of the series are given by 4*3^(n-1)

so, we have 4*3^(15-1) = 4*3⁽¹⁴⁾ = 19,131,876

CPhill · Answer 3 · 2014-05-08T04:25:22

Sorry....Anonymous is correct......I forgot that we were finding a sum !! My bad !!

Thumbs down for me, and Thumbs up for Anonymous.....

Melody · Answer 4 · 2014-05-09T04:43:42

Thank you Chris