Item1.2.5.3.b

Here is an example.

\begin{equation*} \left[\begin{array}{rrr|r} 1 \amp 0 \amp -2 \amp 0 \\ 0 \amp 1 \amp 1 \amp 0 \\ 0 \amp 0 \amp 0 \amp 1 \\ \end{array}\right]\text{.} \end{equation*}
in-context