Thanks to Mathjax, you can use LaTeX equations. Simple inline equations like $f(x) = ax+b$ can be written simply by using

$f(x) = ax + b$

while displayed equations just like \[ f(t) = \frac{a_0}{2} + \sum\limits_{n=0}^{\infty} \left[a_n \mathrm{cos}(\omega_n t) + \mathrm{sin}(\omega_n t) \right] \] can be done by typing

 \\[ f(t) = \frac{a_0}{2} + \Sum\limits_{n=0}^{\infty} \left[a_n \mathrm{cos}(\omega_n t) + \mathrm{sin}(\omega_n t) \right]. \\]

Numbered equations can be done by using \tag{} inside equation environment as show in \[ \vec{F} = m \ddot{\vec{r}}, \tag{1} \label{eq:sample} \]

by using

\\[
\vec{F} = m \ddot{\vec{r}} \tag{1} \label{eq:sample}
\\]

Thus the equation can be referenced by using \ref{} latex command. For exemple, the eq. ($\ref{eq:sample}$) is referenced by using $\ref{eq:sample}$

For more information see Mathjax documentation