Posted by Kelly on Monday, January 11, 2010 at 9:04am.
Find the sum of the first four terms of the geometric sequence with a = 3 and r = 3.
I have NO idea how to attempt to solve this. I do not want an answer just instuctions. Thanks

Algebra  drwls, Monday, January 11, 2010 at 10:13am
The terms in the sequence are presumably
a*r^n.
I rceommend that you read
http://en.wikipedia.org/wiki/Geometric_progression
The first four terms would be (starting with n=0),
a, a r, ar^2 and a r^3.
The sum is a (1 + r + r^2 + r^3)
3 * (1 + 3 + 9 + 27)
= 120
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