Latex 方程组

注意{amsmath}包的引入

1. 不标号方程组

\usepackage{amsmath}

$$
    \begin{cases}
        l_{11}y_{1} = 1 \\
        l_{21}y_{1} + l_{22}y_{2} = 0 \\ 
        l_{31}y_{1} + l_{32}y_{2} + l_{33}y_{3} = 0 \\
        l_{41}y_{1} + l_ {42}y_{2} + l_{43}y_{3} + l_{44}y_{4} = 0
    \end{cases}
$$

or:

\usepackage{amsmath}

\begin{equation*}
     \begin{cases}
         l_{11}y_{1} = 1 \\
         l_{21}y_{1} + l_{22}y_{2} = 0 \\ 
         l_{31}y_{1} + l_{32}y_{2} + l_{33}y_{3} = 0 \\
         l_{41}y_{1} + l_ {42}y_{2} + l_{43}y_{3} + l_{44}y_{4} = 0
     \end{cases}
 \end{equation*}

$$\{\begin{array}{l}{l}_{11}{y}_1=1\\ l_{21}{y}_1+l_{22}{y}_2=0\\ l_{31}{y}_1+l_{32}{y}_2+l_{33}{y}_3=0\\ l_{41}{y}_1+l_{42}{y}_2+l_{43}{y}_3+l_{44}{y}_4=0\end{array}$$
 

2. 标号方程组

(1)方程组整体标号

\usepackage{amsmath}

\begin{equation}
    \begin{cases}
        l_{11}y_{1} = 1 \\
        l_{21}y_{1} + l_{22}y_{2} = 0 \\ 
        l_{31}y_{1} + l_{32}y_{2} + l_{33}y_{3} = 0 \\
        l_{41}y_{1} + l_ {42}y_{2} + l_{43}y_{3} + l_{44}y_{4} = 0
     \end{cases}
\end{equation}

(2)方程组中的每一行方程都标号

\usepackage{cases}

\begin{numcases}{}
    l_{11}y_{1} = 1 \\
    l_{21}y_{1} + l_{22}y_{2} = 0 \\ 
    l_{31}y_{1} + l_{32}y_{2} + l_{33}y_{3} = 0 \\
    l_{41}y_{1} + l_ {42}y_{2} + l_{43}y_{3} + l_{44}y_{4} = 0
\end{numcases}