SOLUTION: What is Sn of the geometric series with a1 = 4, an = 256 and n = 4?

SOLUTION: What is Sn of the geometric series with a1 = 4, an = 256 and n = 4?

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Question 3977: What is Sn of the geometric series with a1 = 4, an = 256 and n = 4?
Answer by longjonsilver(2297) (Show Source): You can put this solution on YOUR website!

need to find r. We know a=4 and that the fourth term, ar^3 = 256 --> r^3 = 64, so r = cube root of 64, so r=4.

So, now:

Sn = 340

this is easy to check in this case, since the GP is small: 4+16+64+256 = 340.

jon.
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