A Triangle is the 2-simplex. The study of triangles is called trigonometry. Its Bowers acronym is "trig".

Types of Triangle

By Sides


When all of the angles and edges of a triangle are equal a triangle is equilateral. Each angle must have a measure of exactly 60 degrees.


When a triangle has two equal sides, it is isosceles. It must also have two equal angles.


A triangle with three unique side lengths is known as a scalene triangle.

By Angles


A triangle with all three angles smaller than 90 degrees is called an acute triangle. All equilateral triangles are also acute triangles.


A triangle with one right angle is a right-angled triangle. Their side lengths follow the equation

, where c is the edge length of the side opposite the right angle.


A triangle where at least one angle is greater than 90 degrees is called an obtuse triangle.

Special Cases

A triangle with more than one right angle is usually degenerate, but can appear on the surface of a sphere. The same applies to a triangle with angles that sum to greater than 180 degrees, and to triangles that have any angle equal to 180 degrees.

See Also

Zeroth First Second Third Fourth Fifth Sixth Seventh Eighth Ninth Tenth Eleventh Twelfth Thirteenth Fourteenth Fifteenth Sixteenth
Simplex Point Line Triangle Tetrahedron Pentachoron Hexateron Heptapeton Octaexon Enneazetton Decayotton Hendecaxennon Dodecadakon Tredecahendakon Quattuordecadokon Quindecatradakon Sexdecateradakon Septendecapetadakon
Hypercube Point Line Square Cube Tesseract Penteract Hexeract Hepteract Octeract Enneract Dekeract Undekeract Dodekeract Tredekeract Quattuordekeract Quindekeract Sexdekeract
Cross Point Line Square Octahedron Hexadecachoron Pentarss Hexarss Heptarss Octarss Ennearss Decarss Hendecarss Dodecarss Tredecarss Quattuordecarss Quindecatrarss Sexdecaterarss
Hypersphere Point Line Circle Sphere Glome Hyperglome Hexaphere Heptaphere Octaphere Enneaphere Decaphere Hendecaphere Dodecaphere Tredecaphere Quattuordecaphere Quindecatraphere Sexdecateraphere
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