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:

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