Square
In Euclidean geometry, a square is a regular quadrilateral, which means that it has four sides of equal length and four equal angles (90- degree angles, π/2 radian angles, or right angles). It can also be defined as a rectangle with two equal-length adjacent sides. It is the only regular polygon whose internal angle, central angle, and external angle are all equal (90°), and whose diagonals are all equal in length. A square with vertices ABCD would be denoted ◻ {\displaystyle \square } ABCD.
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