how to have a matrix on latex code example

Example 1: matrix latex

\begin{bmatrix}
1 & 2 & 3 \\
a & b & c \\
a & b & c \\
\end{bmatrix}

Example 2: how to write a matrix latex

\documentclass{article}
\usepackage{amsmath}
\begin{document}

\[
M=
  \begin{bmatrix}
    1 & 2 & 3 & 4 & 5 \\
    3 & 4 & 5 & 6 & 7
  \end{bmatrix}
\]

\end{document}