Transfer function: from poles and zeros to polynomial coefficients
In short: $(0.937)^2=0.878$

A bit more detail:

$$\begin{align}(z-re^{j\theta})(z-re^{-j\theta})&amp;=z^2-r\left(e^{j\theta}+e^{-j\theta}\right)z+r^2\\&amp;=z^2-2r\cos(\theta)z+r^2\end{align}$$