display style formulas can be obtained as in the standard latex syntax by typing them between double dollars or escaped square brackets ($$ ... $$ or \[ ... \] );

inline style formulas use the slightly non-standard syntax \(... \) or \( ... \).

Examples:

\(e^{i\pi} + 1 = 0\) is rendered as \(e^{i\pi} + 1 = 0\);

\(\int_0^1 x dx = \frac12\) is rendered as \(\int_0^1 x dx = \frac12 \);

finally $$\|z\| = 0$$ is rendered as $$\|z\| = 0.$$

You can freely use mathematical formulas in comments and posts.