\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.
The command \lefteqn is used for splitting long formulas across
lines. It typesets its argument in display style flush left in a box of
zero width.