\documentclass{jarticle}
\usepackage{amsmath}
\usepackage{dotseqn}
\usepackage{empheq}

\begin{document}

\begin{equation}\label{eq:eq01}
   \left\{
   \begin{array}{l}
3x+y= 9 \\
x+3y= 0 
   \end{array}
   \right.
\end{equation}

連立方程式\eqref{eq:eq01}

\begin{equation}\label{eq:eq02}
   \left\{
   \begin{aligned}
c_{11}x_1+\cdots+c_{1n}x_n&= d_1 \\
    \shortvdotswithin{=}
c_{k1}x_1+\cdots+c_{kn}x_n&= d_k 
   \end{aligned}
   \right.
\end{equation}

連立方程式\eqref{eq:eq02}

\end{document}
