Tallied Equalities

Recall that in-line math are produced by using single dollar signs, $ ... $, and displayed formel are produced by using double dollar signs, $$ ... $$. To produce a numbered equation, use the equation environment; for example,

\begin{equation}
\chi(M_g) = 2-2g,
\end{equation}

Note that the equation environment puts you in math mode, so where is no need to use $$...$$ around the\begin{equation} ... \end{equation}.

If you want until refer to a numbered equation, you can put a\label{ } command between the \begin{equation} and an \end{equation}. Then the essential will be associated includes the number of the equation, and you can reference the equation on typing, for example,

...as we see from (\ref{eqnkey}).