%% 
%%  \protect \LaTeX  -Referenz, 1. Auf"|lage 2007
%% 
%%  Example 7-6-10 on page 116.
%% 
%%  Copyright (C) 2007 Herbert Voss
%% 
%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
%% 
%%  See http://www.latex-project.org/lppl.txt for details.
%% 

\documentclass{ttctexa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{355.65944pt}
\setlength\parindent{0pt}
\StartShownPreambleCommands
\usepackage{amsmath,xcolor}
\newcommand*\dx{\mathrm{d}x}
\StopShownPreambleCommands
\begin{document}
\begin{flalign}  f(x) & = \int\frac{1}{x^2}\,\dx \end{flalign}
\begin{flalign}
  f(x) & = \color{magenta}\int\frac{1}{x^2}\,\dx & % <-- dummy &
\end{flalign}
\end{document}