答案1
答案2
使用数组(简单有效):
\documentclass[12pt,a4paper]{article}
\usepackage{amsmath}
\begin{document}
\[\setlength\arraycolsep{1pt}
\begin{array}{rll}
\text{Then } x & = a_0y & \text{for some } y \in D\\
& = a_0uy & = a_0yu\\
& & = xu
\end{array}
\]
\end{document}
附录: 考虑西格尔评论:
\documentclass[12pt,a4paper]{article}
\usepackage{amsmath}
\begin{document}
\[\setlength\arraycolsep{1pt}
\begin{array}{rlcl}
\text{Then } x & = a_0y & &\text{for some } y \in D\\
& = a_0uy & = &a_0yu\\
& & = &xu
\end{array}
\]
\end{document}