e^{ i \theta_1} = \cos{\theta_1} + i \sin{\theta_1}

\[ \frac{\partial^2 u}{\partial x^2}= \frac{1}{c^2} \frac{\partial^2 u}{\partial t^2} \]

Sometimes it is important not to leave a blank line before the ending a math mode display.

Formulas can also be displayed inline by enclosing in $ signs; e.g. .

$f(x) =\frac{d}{dx} \int_a^x f(t) \ dt$