1. Oct 13, 2009

lom

$$\sum \frac{n^2}{3^nz^n}\\$$

$$\frac{1}{R}=\lim_{n->\infty}\sqrt[n]{|\sum \frac{n^2}{3^nz^n}|}\\$$

what to do now?

2. Oct 13, 2009

Staff: Mentor

What's the question? Also, I don't believe that your formula for 1/R is correct.