# Simon Haykin book question

Currently in the book on p. 19 (Neural Networks and Learning Machines Third Edition) I see:

Using the binomial expansion for $(1 - wz^{-1})^{-1}$ , we may rewrite it as $\sum_{l=0}^{\infty}w^{l}z^{-l}$. How Simon did that?

I suppose, that progression is connected to this rewriting. Hence, first formula is just the sum of an infinite decreasing geometric progression with $1$ as $b_{1}$ and $wz^{-1}$ as q.