Answer
$$\left[\begin{array}{r}{-1}&{0}&{2} \\ {1}&{-1}&{0}\\
{0}&{1}&{1} \end{array}\right]\left[\begin{array}{r}{x_1} \\ {x_2}\\{x_3} \end{array}\right]=\left[\begin{array}{r}{1} \\ {-2}\\
{-1} \end{array}\right].$$
Work Step by Step
The system $$
\begin{aligned} -x_{1}+2 x_{3} &=1 \\ x_{1}-x_{2}&=-2 \\
x_{2}+x_{3}&=-1
\end{aligned}
$$
cam written in the form
$Ax=b$, as follows
$$\left[\begin{array}{r}{-1}&{0}&{2} \\ {1}&{-1}&{0}\\
{0}&{1}&{1} \end{array}\right]\left[\begin{array}{r}{x_1} \\ {x_2}\\{x_3} \end{array}\right]=\left[\begin{array}{r}{1} \\ {-2}\\
{-1} \end{array}\right].$$
