sample file sect2.tex

The file sect2.tex contains only the contents of Section 2 of the document. The main LaTeX file, MyDoc.tex, inserts the contents of sect2.tex into the document by using the command 
\input set2.tex

A link to the actual file sect2.tex, and some comments about its contents, are at the bottom of this page.

\section{Math formulae}				% file "sect2.tex"

This is the second section.
As mentioned above, mathematical formulae
may appear in different contexts.

\subsection{Unnumbered formulae}

The simplest formulae appear within the lines of ordinary
text, for example the simple formula $A=\pi r^2$ or just
the variable $x$.  Simply surround the formula with
dollar signs (\$) and \LaTeX{} does the appropriate
thing, italicizing variables, recognizing the macros
for Greek letters and math symbols, etc.
By the way, if you want a dollar sign in your document
(to indicate money, like \$25), you must use the
macro \verb9\$9.

Often a formula needs to be displayed on a separate line
but does not need to be numbered.  In that case,
surround the formula with \emph{double}
dollar signs (\$\$), e.g.,
$$  V = \frac{4\pi r^3}{3}. $$


\subsection{Numbered equations}

For equations to be numbered, use the
\emph{equation environment}
by using
\verb9\begin{equation}9
and
\verb9\end{equation}9
to preceed and end an equation.
\LaTeX{} takes care of numbering equations in order.
\begin{equation}
	\int_{x=1}^{\infty} \frac{1}{(1+x)^2} = \frac{1}{2}
\end{equation}
\begin{equation}
	\sum_{n=1}^{\infty} \frac{1}{(1+n)^2} = \frac{\pi^2}{6}-1
\end{equation}


\subsection{Aligned equations}

For document with a lot of equations it is common to have
a set of equations which should be displayed neatly aligned.
For that, use the ``eqnarray'' environment; surround the
entire set with the commands
\verb9\begin{eqnarray}9 and
\verb9\end{eqnarray}9,
triggering a new formula line with double backslashes
\verb9\\9.
\begin{eqnarray}
A_{\mathrm{\footnotesize circle}} &=& \pi r^2  \\
A_{\mathrm{\footnotesize ellipse}} &=& \pi r_1 r_2
	~ ~ ~ \mbox{(minor and major axes)}
	\\
A_{\mathrm{\footnotesize trapezoid}} &=& \frac12 h(b_1+b_2)
\end{eqnarray}

Any or all of the equation numbers can be suppressed
\cite{Ta} if you wish.

LINKS

Because the character `$' has such a special meaning in LaTeX, you cannot use it to designate money unless you preceed it with a backslash, e.g., ``Pay only \$39.95!''. For many folks, mistakes with the `$' character are the most common source of error messages when compiling a LaTeX document. (The most frequent such error is the use of a non-matching `$' character.)

For a full description of mathematical notation you have to get a LaTeX book; however, the 4-page PDF file Symbols.pdf has a succinct listing of many symbol macros.