\begin{bmatrix} 1 & 2 & 3 \\ a & b & c \\ a & b & c \\ \end{bmatrix}
Trying to typeset an inline matrix here $\begin{pmatrix} a & b\\ c & d \end{pmatrix}$ but it looks too big, so let's try $\big(\begin{smallmatrix} a & b\\ c & d \end{smallmatrix}\big)$ instead.
