This article will show on how to display formulas (mathematics equations) inside a box or frame.
Using \fbox and \parbox
The formula will be framed. Must declare the width of the frame.
\fbox
{
\parbox{5cm}
{
\[
\oint\limits_C V\,d\tau =
\oint\limits_\Sigma\nabla\times V\,d\sigma
\]
}
}

Using \fbox and \minipage
The formula will be framed. Must declare the width of the frame.
\fbox
{
\begin{minipage}[position]{5cm}
\[
\oint\limits_C V\,d\tau =
\oint\limits_\Sigma\nabla\times V\,d\sigma
\]
\end{minipage}
}

Using equation environment and \fbox
The formula will be centred, framed and numbered.
\begin{equation}
\fbox
{
$ \displaystyle
\oint\limits_C V\,d\tau =
\oint\limits_\Sigma\nabla\times V\,d\sigma
$
}
\end{equation}

Using displaymath enviroment and \fbox
The formula will be centred, framed and unnumbered.
\begin{displaymath}
\fbox
{
$ \displaystyle
\oint\limits_C V\,d\tau =
\oint\limits_\Sigma\nabla\times V\,d\sigma
$
}
\end{displaymath}

