\documentclass{article}
%to show line numbers, go to TOOLS, OPTIONS, EDITOR and check the box SHOW LINE NUMBERS

\begin{document}

$$\left( \frac{x}{2} - x ) = 0$$
%ERROR: right-hand delimeter missing

$$x = \frac{b^2-4ac){2a}$$
%ERROR: mismatched delimiter {)

$$t = \sqrt{\frac{x-z}{a}$$
%ERROR: missing } to close the sqrt{ command

\begin{enumerate}
\item First
\item Second
	\begin{enumerate}
	\item Sub1
	\item Sub2
	%ERROR: missing \end{enumerate}
\item Third
\end{enumerate}

$$\farc{3}{4}$$
%ERROR: misspelled \frac{}{} command

The discriminant of a quadratic is $b^2 - 4ac.  If that discriminant
is negative, then ther are no real roots.
%ERROR: missing closing $ to end MATH MODE

\end{document}