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

Types of Triangle

By Sides

Equilateral

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.

Isosceles

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

Scalene

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

By Angles

Acute

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

Right-Angled

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.

Obtuse

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
Simplex Point Line Triangle Tetrahedron Pentachoron Hexateron Heptapeton Octaexon Enneazetton Decayotton Hendecaxennon
Hypercube Point Line Square Cube Tesseract Penteract Hexeract Hepteract Octeract Enneract Dekeract
Cross Point Line Square Octahedron Hexadecachoron Pentarss Hexarss Heptarss Octarss Ennearss Decarss
Hypersphere Point Line Circle Sphere Glome Hyperglome Hexaphere Heptaphere Octaphere Enneaphere Decaphere
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