$10\ Array\ environment,examples$
$\left( \begin{array}{cc} 2\tau & 7\phi-frac5{12} \\ 3\psi & \frac{\pi}8 \end{array} \right) \left(\begin{array}{c} x \\ y \end{array} \right) \mbox{and} \left[ \begin{array}{cc|r}3 & 4 & 5 \\ 1 & 3 & 729 \end{array} \right]$
$f(z) = \left \{ \begin{array}{rcl} \overline{\overline{z^2}+\cos z} & \mbox{for} & |z|<3 \\ 0 & \mbox{for} & 3\leq|z|\leq5 \\ \sin\overline{z} & \mbox{for} & |z|>5\end{array} \right.$