Sorry I understand this now. The expansion was about z=i, but I understand you would just the distance between the place you are expanding around and the closest singularity.
< Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown >
How would you find the radius of convergence for the taylor expansion of:
\begin{equation} f(z)=\frac{e^z}{(z-1)(z+1)(z-3)(z-2)} \end{equation}
I was thinking that you would just differentiate...