Power series question (ROC)

hello,

I see now that i did these power series by pattern and now I'm stuck big time :D

Problem is ...

$\displaystyle \displaystyle \sum_{n=1}^{\infty} \frac {n}{3^nx^{2n}}$

so i found R as

$\displaystyle \displaystyle R = \lim_{n\to \infty} \big{|} \frac {a_n}{a_{n+1}}\big{|} = ... = 3$

and than i sow x is at power -2n and here is my problem...

should I do it like this : (to see region of convergence)

$\displaystyle \displaystyle |x|< 3 $

or like this ...

$\displaystyle \displaystyle |x^{-2}|< 3 $

$\displaystyle \displaystyle |x|< \frac{1}{\sqrt{3}}$

or I am way of with this ?

can someone please explain to me what to do when i have "x" like i do here :D

thanks in advance :D