\begin{itemize}
\item Es gilt \(a + b = b + a\).
\end{itemize}
\documentclass[11pt,a4paper,ngerman]{article}
\usepackage[T1]{fontenc}
\usepackage{babel}
\usepackage[tbtags]{mathtools}% lädt »amsmath« und behebt seine Fehler
\usepackage{libertinus,libertinust1math}% gewünschte Ausgabe
\usepackage{microtype}
\begin{document}
\begin{itemize}
\item Es gilt
\begin{flalign}
a + b &= b + a & \\
c + d + e &= e + d + c &
\end{flalign}.
\end{itemize}
\end{document} \documentclass[11pt,a4paper,ngerman]{article}
\usepackage[T1]{fontenc}
\usepackage{mathtools}
\begin{document}
\begin{itemize}
\item
\begin{flalign}
\text{Es gilt }a + b = b + a\text{.}\hfill&&
\end{flalign}
\end{itemize}
\end{document}
\documentclass{article}
\usepackage{mathtools}
\usepackage{showframe}
\newcommand{\eqNum}{\stepcounter{equation}(\theequation)}
\begin{document}
\begin{flalign}
\hspace{5.3mm}\bullet&\text{ Es gilt } a + b = b + a.&&\\
\bullet&\ a + b + c + d = d + c + b + a.&&
\end{flalign}
\begin{itemize}
\item Es gilt $a + b = b + a.$\hfill\eqNum
\item $a + b + c + d = d + c + b + a.$\hfill\eqNum
\end{itemize}
\end{document}\documentclass[11pt,a4paper,ngerman]{article}
\usepackage[T1]{fontenc}
\usepackage{mathtools}
\newcommand{\eqnum}{\stepcounter{equation}(\theequation)}
\begin{document}
\begin{itemize}
\item Es gilt \(a + b = b + a\).\hfill\eqnum
\end{itemize}
\end{document}