\documentclass{article}

\begin{document}

$$\left( \frac{x}{2} - x ) = 0$$

$$x = \frac{b^2-4ac){2a}$$

$$t = \sqrt{\frac{x-z}{a}$$


\begin{enumerate}
\item First
\item Second
	\begin{enumerate}
	\item Sub1
	\item Sub2
\item Third
\end{enumerate}

$$\farc{3}{4}$$

The discriminant of a quadratic is $b^2 - 4ac.  If that discriminant
is negative, then there are no real roots.

\end{document}