In geometry, a **quadrilateral** is a polygon with four **sides** or **edges** and four **vertices** or **corners**. Sometimes, the term **quadrangle** is used, for etymological symmetry with triangle, and sometimes **tetragon** for consistency with pentagon (5 sided), hexagon (6 sided) and so on. However, the term quadrangle could be considered incorrect, as the laws of Euclid state that an angle's degree measure must be less than 180, and so a concave quadrilateral has only 3 angles. The word quadrilateral can mean: In geometry, a quadrilateral is a polygon with 4 sides. ...
For other uses, see Geometry (disambiguation). ...
Look up polygon in Wiktionary, the free dictionary. ...
A triangle. ...
Look up pentagon in Wiktionary, the free dictionary. ...
For other uses, see Hexagon (disambiguation). ...
For other uses, see Euclid (disambiguation). ...
In geometry, concavity is a property of certain geometric figures, and in calculus, a property of certain graphs of functions. ...
Quadrilaterals are either simple (not self-intersecting) or complex (self-intersecting). Simple quadrilaterals are either convex or concave. A simple concave hexagon In geometry, two edges of a polygon may cross or even overlap in general. ...
Categories: Stub | Polygons ...
A convex pentagon In geometry, a convex polygon is a simple polygon whose interior is a convex set. ...
In geometry, concavity is a property of certain geometric figures, and in calculus, a property of certain graphs of functions. ...
## Convex quadrilaterals
Convex quadrilaterals are further classified as follows: - Trapezium (British English) or trapezoid (Amer.): two opposite sides are parallel.
- Isosceles trapezium (Brit.) or isosceles trapezoid (Amer.): two opposite sides are parallel, the two other sides are of equal length, and the two ends of each parallel side have equal angles. This implies that the diagonals are of equal length.
- Trapezium (Amer.): no sides are parallel.
- Parallelogram: both pairs of opposite sides are parallel. This implies that opposite sides are of equal length, opposite angles are equal, and the diagonals bisect each other.
- Kite: two adjacent sides are of equal length and the other two sides also of equal length. This implies that one set of opposite angles is equal, and that one diagonal perpendicularly bisects the other. (It is common, especially in the discussions on plane tessellations, to refer to a concave kite as a
*dart* or *arrowhead*.) - Rhombus or rhomb: all four sides are of equal length. This implies that opposite sides are parallel, opposite angles are equal, and the diagonals perpendicularly bisect each other.
- Rhomboid: a parallelogram in which adjacent sides are of unequal lengths and angles are oblique (not right angles).
- Rectangle (or Oblong): all four angles are right angles. This implies that opposite sides are parallel and of equal length, and the diagonals bisect each other and are equal in length.
- Square (regular quadrilateral): all four sides are of equal length (equilateral), and all four angles are equal (equiangular), with each angle a right angle. This implies that opposite sides are parallel (a square is a parallelogram), and that the diagonals perpendicularly bisect each other and are of equal length. A quadrilateral is a square if and only if it is both a rhombus and a rectangle.
- Cyclic quadrilateral: the four vertices lie on a circumscribed circle.
- Tangential quadrilateral: the four edges are tangential to an inscribed circle. Another term for a tangential polygon is
*inscriptible*. - Bicentric quadrilateral: both cyclic and tangential.
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The word trapezium has several meanings: A trapezium refers to either of two geometric figures. ...
British English (BrE, BE, en-GB) is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere in the Anglophone world. ...
This article is about the geometric figure. ...
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Parallel is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. ...
An isosceles trapezoid (isosceles trapezium in British English) is a quadrilateral with a line of symmetry bisecting one pair of opposite sides. ...
An isosceles trapezoid. ...
This article is about angles in geometry. ...
The word trapezium has several meanings: A trapezium refers to either of two geometric figures. ...
A parallelogram. ...
A kite showing its equal sides and its inscribed circle. ...
A tessellated plane seen in street pavement. ...
Two rhombi. ...
These shapes are Rhomboids In geometry, a rhomboid is a parallelogram in which adjacent sides are of unequal lengths and angles are oblique. ...
Oblique can mean one of several things: In linguistics, oblique case. ...
In geometry, a rectangle is defined as a quadrilateral where all four of its angles are right angles. ...
In geometry, a rectangle is a defined as a quadrilateral polygon in which all four angles are right angles. ...
For other uses, see Square. ...
In geometry, a cyclic quadrilateral is a quadrilateral whose vertices all lie on a single circle. ...
Tangential quadrilateral. ...
Diagram for quadrilateral. ...
## More quadrilaterals - An arrowhead has bilateral symmetry like a kite, but the top concaves inwards.
- A self-intersecting quadrilateral is called variously a
**cross-quadrilateral**, **butterfly quadrilateral** or **bow-tie quadrilateral**. - An equiangular quadrilateral is a rectangle if convex, and an "angular eight" with corners on a rectangle if non-convex.
- A quadrilateral whose vertices do not all lie in a flat plane is a
**skew quadrilateral**. In geometry, a rectangle is defined as a quadrilateral where all four of its angles are right angles. ...
## Taxonomy A taxonomy of quadrilaterals is illustrated by the following graph. Lower forms are special cases of higher forms. Note that "trapezium" here is referring to the British definition (the American equivalent is a trapezoid). For the science of classifying living things, see alpha taxonomy. ...
Hierarachy of quadrilaterals. ...
## External links |