Absolute stability region
Stable region in red.

Coefficients

\begin{align} \begin{array}{c|ccc} & & & \\ 1 & 1 & & \\ \frac{1}{2} & \frac{1}{4} & \frac{1}{4} & \\ \hline & \frac{1}{6} & \frac{1}{6} & \frac{2}{3} \end{array}\end{align}

Properties