需要帮助解决跨越多行的问题

Question

如何输入横跨三条线/方程的垂直线？谢谢！

Answer 1

另外三种解决方案，基于aligned环境。第三种解决方案使用环境，这是@Gonzalo Medina 提供的环境dlrcases的扩展：drcasesmathtools

\documentclass{article}
\usepackage{empheq}%
\usepackage{array, setspace}

\makeatletter
\newcases{dlrcases}{\quad}{%
  $\m@th\displaystyle{##}$\hfil}{$\m@th\displaystyle{##}$\hfil}{\lbrace}{\rbrace}
\newcases{lrcases}{\quad}{%
  $\m@th{##}$\hfil}{{##}\hfil}{\lbrace}{\rbrace}
\makeatother

\begin{document}

\[
  \left\{\setstretch{0.7}\begin{array}{@{}c|c@{\,}}
  \begin{aligned}
    x & \geq 0 \\
    y & \geq 0 \\
    x & \leq 5
  \end{aligned}
  &\! \begin{aligned}
  x+y & \leq 7\\
  x+2y & \geq 4\\
  y &\leq x+5
  \end{aligned}
  \end{array}
  \right\}
\]

\begin{empheq}[left=\empheqlbrace, right=\empheqrbrace]{equation*}
\begin{array}{@{}c|c@{}}
  \begin{aligned}
    x & \geq 0 \\
    y & \geq 0 \\
    x & \leq 5
  \end{aligned}
  &\! \begin{aligned}
  x+y & \leq 7\\
  x+2y & \geq 4\\
  y &\leq x+5
  \end{aligned}
  \end{array}
\end{empheq}

\[ \begin{dlrcases}
      \begin{array}{@{\!}c|c@{}}
  \begin{aligned}
    x & \geq 0 \\
    y & \geq 0 \\
    x & \leq 5
  \end{aligned}
  &\! \begin{aligned}
  x+y & \leq 7\\
  x+2y & \geq 4\\
  y &\leq x+5
  \end{aligned}
  \end{array}
\end{dlrcases} \]

\end{document} 

Answer 2

\documentclass{article}
\usepackage{array}

\begin{document}
\[
\left\{\begin{array}{c|r@{\;}l}
x\geq 0 & x+y & \leq 7\\
y\geq 0 & x+2y & \geq 4\\
x\leq 5 & y &\leq x+5\\
\end{array}
\right\}
\]
\end{document}