TeX source:
\underline{A}_{r}=\left(\begin{array}{rrrr|r}1, & 3, & -1, & 2& 5\\0, & -1, & 4, & -1& 0\\2, & 2, & 1, & 0& -1\\2, & 6, & 0, & 5& 7\end{array}\right);