我想用我自己的编号对系统中的每个方程进行编号，也为系统编号

Question

在这张图片中，我想用 (a) 来数字化方程 xy=1，用 (b) 来数字化第二个方程，用 (1) 来数字化系统

Answer 1

\documentclass[12pt,a4paper]{article}

\usepackage{amsmath}
\usepackage{cases}

\begin{document}

Half-hearted recommendation
\begin{subnumcases} {\label{system}}
  x-y = 1\label{x}\\
  2\,x-y=3 \label{y}
\end{subnumcases}
Provide the solution to equation (\ref{system}) subtracting
(\ref{x}) from (\ref{y}).

But if you must have three separate numbers, you could put them in by
hand where cases expects a qualification
\begin{equation}
\label{system2}
  \begin{cases} 
  x-y = 1 &\qquad \text{(a)}\\
  2\,x-y=3&\qquad \text{(b)}
  \end{cases}
\end{equation}
But those braces don't seem appropriate at all.
\begin{equation}
\label{system3}
\begin{aligned}
   x-y &= 1 &\qquad& \text{(a)}\\
 2\,x-y&= 3 &\qquad& \text{(b)}
\end{aligned}
\end{equation}
but probably best is this
\begin{subequations}
\label{system4}
  \begin{align}
   x-y &= 1 \label{xx}\\
 2\,x-y&= 3 \label{yy}
\end{align}
\end{subequations}
combined eq.~(\ref{system4}).
What it sounds like you are asking for is this atrocity
\begin{align}
  x-y &= 1 \tag{a}\\
      &           \\
 2\,x-y&= 3 \tag{b}
\end{align}
which looks awful.

\end{document}