# Maclaurin Series used to find associated radius of convergence Q!

1. Dec 11, 2005

I have the Maclaurin series for cos (x), is their a way to find its radius of convergence from that?

ALSO
Is there a trick to find the shorter version of the power series for the Maclaurin series, I can never seem to find it so instead of the long series with each term but like E summation (the series)

Last edited: Dec 11, 2005
2. Dec 11, 2005

### shmoe

you can try the ratio test.

Err, do you mean writing the series using the sigma notation instead of the first few terms followed by some ...? You want to look for patterns in the coefficients. No real trick, practice will help though.

3. Dec 11, 2005

Yeah i tried the ratio test, but the radius of convergence it sayed in the big is infinity, how is that possible as it has to be n < 1?

4. Dec 11, 2005

### shmoe

I don't understand what you're saying, what's "in the big" mean? What are you calling n that it has to be less than 1?

5. Dec 11, 2005