Find a power series expression $\sum_{n=0}^\infty A_n z^n $ for $ \frac{1}{z^2-\sqrt2 z +2} $
I'm completely stuck on this question. I know how to manipulate power series but I've never had to find one from such a complicated function. Also we're asked to find the radius of convergence although this I think I can do. Also I know that maybe the Taylor series expansion could help but differentiating that function leads to an awful mess.