posted by Kelly on .
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
The terms in the sequence are presumably
I rceommend that you read
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)