Equations can get reference numbers using the
\tag{} macro, e.g:
\[E=mc^2\tag{1}\]
produces
\[E=mc^2\tag{1}\]
Note that the contents of \tag{} are in text mode, so if you
want to include math symbols, use \tag{$...$}. E.g.,
\[E=mc^2\tag{$\bullet$}\]
produces
\[E=mc^2\tag{$\bullet$}\]
\begin{equation}
(x-aw)^2 +(y-bw)^2 =r^2w^2.
\tag{2}
\end{equation}
