如何在不影响方程对齐的情况下插入句点？

Question

这是我当前的设置：

\[\triangle A_{1}B_{1}C_{1}\sim\triangle A_{2}B_{2}C_{2}\]
\[\Big\Downarrow\]
\vspace{-1.75em}
\begin{align}
    \angle C_{1}A_{1}B_{1}&=\anglen C_{2}A_{2}B_{2}\\
    \angle A_{1}B_{1}C_{1}&=\angle A_{2}B_{2}C_{2}\\
    \angle B_{1}C_{1}A_{1}&=\angle B_{2}C_{2}A_{2}.
\end{align}

但是，方程式末尾的句号会导致环境偏移。我尝试将整个东西放在对齐环境中，但垂直箭头似乎无法正确对齐到中心。

编辑：我明白了，放在\rlap{.}最后就行了，谢谢！

Answer 1

您可以将它们全部放在一个align环境中，如果您确实想将向下箭头居中\shortintertext，则可以使用 。可以说更好的选择是定义\vdotswithinfrom的变体mathtools。

\documentclass{article}
\usepackage{mathtools}
\newcommand\Whaterverwithin[2]{%
\mathmakebox[\widthof{\ensuremath{{}#1{}}}][c]{{#2}}}
\begin{document}
\begin{align}
\triangle A_{1}B_{1}C_{1}&\sim\triangle A_{2}B_{2}C_{2}\notag\\
\shortintertext{\hfill$\displaystyle\big\Downarrow$\hfill\mbox{}}
    \angle C_{1}A_{1}B_{1}&=\angle C_{2}A_{2}B_{2}\\
    \angle A_{1}B_{1}C_{1}&=\angle A_{2}B_{2}C_{2}\\
    \angle B_{1}C_{1}A_{1}&=\angle B_{2}C_{2}A_{2}.
\end{align}

\begin{align}
\triangle A_{1}B_{1}C_{1}&\sim\triangle A_{2}B_{2}C_{2}\notag\\
& \Whaterverwithin{=}{\displaystyle\big\Downarrow}
\notag\\
    \angle C_{1}A_{1}B_{1}&=\angle C_{2}A_{2}B_{2}\\
    \angle A_{1}B_{1}C_{1}&=\angle A_{2}B_{2}C_{2}\\
    \angle B_{1}C_{1}A_{1}&=\angle B_{2}C_{2}A_{2}\;.
\end{align}
\end{document}