Image: Wikimedia Commons

triangle

Basic three-sided shape of geometry

Entitygeometric shapeQ19821

Also known as 3-gon · 2-simplex

Instance of: geometric shape
Subclass of: bicentric polygon
, simplex
, tritope
+2 more

Overview

From Wikipedia, the free encyclopedia · Read full article · Text CC BY-SA 4.0

A triangle or trigon is a polygon consisting of three sides connected at three corners. It is one of the basic shapes in geometry and the simplest of polygons. The corners, also called vertices, are zero-dimensional points while the sides connecting them, also called edges, are one-dimensional line segments. A triangle has three internal angles, each one bounded by a pair of adjacent sides; the sum of angles of a triangle always equals a straight angle. The triangle is a plane figure and its interior is a planar region. Sometimes an arbitrary edge is chosen to be the base, in which case the opposite vertex is called the apex; the shortest segment between the base and apex is the height. The area of a triangle equals one-half the product of height and base length.

Overview

All data

86 statements · 12% with external sources · numbers in brackets are citations

Unicode character: 🔺
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Has facet polytope: edge quantity: 3
Has characteristic: plane area defining formula: A=\frac{1}{2}bh, S= {1 \over 4}\sqrt{(a+b+c)(b+c-a)(a+c-b)(a+b-c)}
perimeter defining formula: P=a+b+c
triangle inequality theorem
area of a triangle
Different from: equilateral triangle
scalene triangle
isosceles triangle
Followed by: quadrilateral applies to part: polygon
tetrahedron applies to part: simplex
Follows: digon applies to part: polygon
line segment applies to part: simplex
Has vertex figure: line segment quantity: 3
Has part(s) of the class: edge quantity: 3
vertex quantity: 3
base
height
apex
apex-base pair quantity: 3
Union of: list of values as qualifiers list item: equilateral triangle, isosceles triangle
Disjoint union of: list of values as qualifiers list item: right triangle, acute triangle
list of values as qualifiers list item: equilateral triangle, non-equilateral isosceles triangle
list of values as qualifiers list item: equilateral triangle, non-equilateral triangle
list of values as qualifiers list item: isosceles triangle, scalene triangle
list of values as qualifiers list item: right triangle, acute or obtuse triangle
Wikimedia outline: list of triangle topics

On other databases

45 identifiers linking triangle across the web's reference databases

Data quality

statements

12%

externally sourced

Source last edited October 8, 2026. AIDB refreshes this page daily.

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AIDB. (2026). triangle (Q19821). Retrieved from https://aidb.si/e/triangle-Q19821