Math in WordPress has become as easy as $1,2,3,\dots$ thanks to MathJax. Some trigonometric identities:

\begin{gather}
\sin\alpha^2 +\cos\alpha^2 = 1 \\
\sqrt{2}\left|\cos(\alpha/2)\right| = \sqrt{\cos(\alpha) +1}
\end{gather}

The Dirac equation for a relativistic electron:
\begin{equation}
\mathrm{i}\hbar\frac{\partial\Psi(\vec{r}, t)}{\partial t} =
\left(c\vec{\alpha}\cdot\left(\hat{\vec{p}}- q \vec{A}(\vec{r}, t) \right) +
q \phi(\vec{r}, t) + mc^2\beta
\right)\Psi(\vec{r}, t)
\end{equation}