Expand
Expand[expr] expands out products and positive integer powers in expr.
Expand[expr, patt] leaves unexpanded any parts of expr that are free of the pattern patt.
Expand works only on positive integer powers.
Expand applies only to the top level in expr.
Expand[expr, Modulus->p] expands expr reducing the result modulo p.
See The Mathematica Book on the web: Section 1.4.3, Section 1.4.5 and Section 3.3.1.
See also: Distribute, Apart, Series, Factor, LogicalExpand, TrigExpand, PowerExpand, ExpandAll.
Further Examples