=====Boxed equation=====
Define a new command as follows:
<code latex>
\newcommand{\boxedeqn}[1]{%
\[\fbox{%
\addtolength{\linewidth}{-2\fboxsep}%
\addtolength{\linewidth}{-2\fboxrule}%
\begin{minipage}{\linewidth}%
\begin{equation}#1\end{equation}%
\end{minipage}%
}\]%
}
</code>
Here is an example of its use:
<code latex>
\boxedeqn{
X_1(j\omega) =
\int\limits^{+\infty}_{-\infty} x_1(t) e^{-j\omega t} dt
}
</code>
If you dont want to box the equation number, use \boxed{…}