This is an example of an inline formula $ x^2+2 $.
This is an example of a displayed formula:
\[\int_{-\infty}^\infty e^{-\frac{t^2}{2}}\,dt=\sqrt{2\pi}\]
This is the same with a label:

\int_{-\infty}^\infty e^{-\frac{t^2}{2}}\,dt=\sqrt{2\pi}

Please note that a labeled equation can be referenced in the text, e.g. the last formula was (\ref{gaussian}).

Multi-line equation:

\int \ln x \;dx &= \int 1 \cdot \ln x \;dx \\
&= x \cdot \ln x - \int x \cdot \frac{1}{x} \;dx \\
&= x \cdot \ln x - x + C