Suppose that $P(z)$ and $Q(z)$ are polynomials with no common roots and $\deg(P) < \deg(Q)$. Suppose that $Q(z) = \displaystyle\prod_{k=1}^t (z - z_k)^{n_k}$ then the partial fraction decomposition of $\frac{P(z)}{Q(z)}$ has the form: $ \frac{P(z)}{Q(z)} = \sum_{k=1}^t \sum_{j=1}^{n_k} \frac{a_{kj}}{(z - z_k)^j}$ Show that $ a_{kj} = \operatorname{Res}_{z_k} ((z - z_k)^{j-1} \frac{P(z)}{Q(z)})$
I am having a hard time answering this question could someone shed some light?