It didnt say it starts with anything, even if it starts with 1 it still doesnt give you the series does it?(Original post by Simplicity)
No that is wrong. When did it say n=0. I'm pretty sure it starts at n=1 and goes on.
Again, your wrong it works fine without replacing n with n-1.
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Geometric series: sum to infinity watch
- 06-08-2009 17:08
(Original post by ShortRef)
- 06-08-2009 17:12
Can we please go back and actually discuss if the question is right or not.
"Sum the series 1 + 4x + 7x² + 10x³ + ... + (3N - 2)x^N."
so the general term is (3N - 2)x^N
Putting N = 0 gives -2
Putting N = 1 gives (3 - 2)x^1 = x
Putting N = 2 gives (6 - 2)x^2 = 4x^2
Putting N = 2 gives (9 - 2)x^3 = 7x^3
So the series has to be (3n - 2)x^(n-1)
Okay that looks correct.Last edited by Simplicity; 06-08-2009 at 17:16.