squareSquare2001-12-12 00:21:262006-11-03 12:12:12Definition\usepackage{amssymb}
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A \emph{square} is the regular 4-gon, that is, a quadrilateral whose 4 angles and 4 sides are respectively equal. Each angle of a square must be a right angle.
This implies a square is a parallelogram that is both a rhombus and a rectangle at the same time.
Notice, however, that if a quadrilateral has its 4 sides equal, we cannot generally say it is a square, since it might be a rhombus as well.
If $r$ is the length of a side, the diagonals of a square (which are equal since it's a rectangle too) have length $r\sqrt{2}$.
\includegraphics{square}