$$
#mimetex("\Large\begin{pmatrix} x+y+z&=&3\\ 2y&=&x+z\\2x+y&=&z\end{pmatrix}");
#mimetex("X=\begin{pmatrix} a&b\\ c&d\end{pmatrix}"); $$
#mimetex("\Large\begin{array}{rccclBCB}&f& \longr[75]^{\alpha:{\normalsize f\rightar~g}}& g\\ \large\gamma&\longd[50]&&\longd[50] & \large\gamma\\ &u&\longr[75]_\beta&v\end{array}");
#mimetex("\Large\left.\begin{eqnarray} x+y+z&=&3\\ 2y&=&x+z\\2x+y&=&z\end{eqnarray}\right\}");
#mimetex("\Large\overbrace{a,...,a}^{\text{k a^,s}}, \underbrace{b,...,b}_{\text{l b^,s}}\hspace{10} \large\underbrace{\overbrace{a...a}^{\text{k a^,s}}, \overbrace{b...b}^{\text{l b^,s}}}_{\text{k+l elements}}");