While setting lecture notes I use a quite wide margin (two side) with a relatively narrow text width. Tables and figures are allowed to use the complete width, if necessary. Now I would like to set an equation using the whole width, which is nearly successful (see MWE below). Only the equation tag sticks still to the textwidth. How can I change this?

\documentclass{scrbook} \usepackage{blindtext} \usepackage[textwidth=12cm, textheight=22cm, includehead=true, includefoot=true, headsep=1.2\baselineskip, marginparsep=0.8cm, marginparwidth=4.2cm, inner=2cm, top=1.5cm ]{geometry} \begin{document} \blindtext % \begin{equation} E = m c^2 \end{equation} % \blindtext % \begin{addmargin*}{0pt}{\marginparsep+\marginparwidth} \begin{equation} EEEEEEEEEEEEEEE = mmmmmmmmmmmmmmmmmmmmmmm c^2 \end{equation} \end{addmargin*} % \blindtext \end{document}