![注释方程式](https://linux22.com/image/479648/%E6%B3%A8%E9%87%8A%E6%96%B9%E7%A8%8B%E5%BC%8F.png)
答案1
使用flalign
and\llap
以便它不会修改主公式的位置:
\documentclass[11pt, leqno]{article}
\usepackage[utf8]{inputenc}
\usepackage{mathtools}
\usepackage{showframe}
\renewcommand{\ShowFrameLinethickness}{0.3pt}
\begin{document}
\begin{flalign}
& & a+k_nr & =a(a^{\varphi(r)})^n & & \llap{(dla $ n=1,2,\ldots $)}
\end{flalign}
\end{document}