We are given a system of equations,
[tex]\begin{cases}-x+2y=0\\y=-2\\ \end{cases}[/tex]
This will translate into a 2x2 matrix of coefficients (because 2 equations and 2 unknowns),
[tex]\begin{bmatrix}-1&2\\0&1\\ \end{bmatrix}[/tex]
The matrix will then be applied to the vector (lower dimensions on top),
[tex]\begin{bmatrix}x\\y\\ \end{bmatrix}[/tex]
And the result vector will be whats on the other side of equals sign,
[tex]\begin{bmatrix}0\\-2\\ \end{bmatrix}[/tex]
So to put everything together,
[tex]\begin{bmatrix}-1&2\\0&1\\ \end{bmatrix}\begin{bmatrix}x\\y\\ \end{bmatrix}=\begin{bmatrix}0\\-2\\ \end{bmatrix}[/tex]
Hope this helps :)
