%% 
%%  An UIT Edition example
%% 
%%  Example 05-03-4 on page 74.
%% 
%%  Copyright (C) 2010 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.
%% 
%% 
%% ==== 
% Show page(s) 1
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\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{153.70511pt}
\setlength\parindent{0pt}
\StartShownPreambleCommands
\usepackage{xcolor,empheq}
\StopShownPreambleCommands
\begin{document}
\begin{empheq}[box=\fcolorbox{blue}{cyan!40}]{align*}
        x(t) & =\frac{a\left(t^{2}-1\right)}{t^2+1}\\
        y(t) & =\frac{at\left(t^{2}-1\right)}{t^2+1}
\end{empheq}
\end{document}