Elgnairt

A Triangle is the -2-simplex. The study of triangles is called trigonometry. Its Bowers acronym is "girt".
==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
-a^2 - -b^2 = -c^2 , 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.
Category:Geometry
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