Latex tips and tricks

Define a new command as follows:

\newcommand{\boxedeqn}[1]{%
  \[\fbox{%
      \addtolength{\linewidth}{-2\fboxsep}%
      \addtolength{\linewidth}{-2\fboxrule}%
      \begin{minipage}{\linewidth}%
      \begin{equation}#1\end{equation}%
      \end{minipage}%
    }\]%
}

Here is an example of its use:

\boxedeqn{
  X_1(j\omega) =
    \int\limits^{+\infty}_{-\infty} x_1(t) e^{-j\omega t} dt
}

If you dont want to box the equation number, use \boxed{…}