MathGloss/M/Matrix

Examples
$$A=\begin{pmatrix} 1 & 3 &-4 \\ 0 & -1 & 5 \\  3 & 4 & 8 \end{pmatrix}$$ is a $$3\times 3$$ matrix

$$B=\begin{pmatrix} 1 & 3 &-4 & 1 \\ 0 & -1 & 5 & 7  \\  3 & 4 & 8 & 2  \end{pmatrix}$$ is a $$3\times 4$$ matrix