Tetragon  (4-gon)also Quadrilateral, Quadrangle
From Greek: tetra "four" + gonia "angle"
Definition: A polygon with 4 sides
also: Quadrilateral and Quadrangle
Try this Adjust the tetragon below by dragging any orange dot. By clicking on the top left command line, you can switch it between a regular and irregular tetragon.

Because a tetragon has an even number of sides, in a regular tetragon, opposite sides are parallel. A regular tetragon is a square.

Properties of regular tetragons

Interior angle 90° Like any regular polygon, to find the interior angle we use the formula   (180n–360)/n . For a tetragon, n=4. See Interior Angles of a Polygon
Exterior Angle 90° To find the exterior angle of a regular tetragon, we use the fact that the exterior angle forms a linear pair with the interior angle, so in general it is given by the formula 180-interior angle. See Exterior Angles of a Polygon
Area s2 Where S is the length of a side. To find the area of a tetragon or any polygon, using various methods, see Area of a Regular Polygon and Area of an Irregular Polygon

Properties of all tetragons

Number of diagonals 2 The number of distinct diagonals possible from all vertices. (In general  ½n(n–3)  ). In the figure above, click on "show diagonals" to see them. See Diagonals of a Polygon
Number of triangles 2 The number of triangles created by drawing the diagonals from a given vertex. (In general n–2). In the figure above, click on "show triangles" to see them. See Triangles of a Polygon
Sum of interior angles 360° In general 180(n–2) degrees . See Interior Angles of a Polygon

Related polygon topics

General

Types of polygon

Area of various polygon types

Perimeter of various polygon types

Angles associated with polygons

Named polygons