_________
_________
\begin{array}{col1col2...coln}
column 1 entry & column 2 entry ... & column n entry \\
.
.
.
\end{array}
Math arrays are produced with the array environment. It has a single
mandatory argument describing the number of columns and the alignment
within them. Each column, coln, is specified by a single letter that
tells how items in that row should be formatted.
c -- for centred
l -- for flush left
r -- for flush right
&. Column entries may include
other LaTeX commands. Each row of the array must be terminated with the
string \\.
Note that the array environment can only be used in math mode, so
normally it is used inside an equation environment.
\begin{eqnarray}
math formula 1 \\
math formula 2 \\
.
.
.
\end{eqnarray}
The eqnarray environment is used to display a sequence of equations or
inequalities. It is very much like a three-column array environment,
with consecutive rows separated by \\ and consecutive items within a
row separated by an &.
An equation number is placed on every line unless that line has a
\nonumber command.
\begin{equation}
math formula
\end{equation}
The equation environment centres your equation on the page and places
the equation number in the right margin.
\begin{theorem}
theorem text
\end{theorem}
The theorem environment produces "Theorem x" in boldface followed by
your theorem text.