Igor's Test #1

A triangle is a figure consisting of three line segments, each of whose endpoints are connected.^[1] This forms a polygon with three sides and three angles. The terminology for categorizing triangles is more than two thousand years old, having been defined in Book One of Euclid's Elements.^[2] The names used for modern classification are either a direct transliteration of Euclid's Greek or their Latin translations.

Triangles have many types based on the length of the sides and the angles. A triangle whose sides are all the same length is an equilateral triangle,^[3] a triangle with two sides having the same length is an isosceles triangle,^[4][a] and a triangle with three different-length sides is a scalene triangle.^[7] A triangle in which one of the angles is a right angle is a right triangle, a triangle in which all of its angles are less than that angle is an acute triangle, and a triangle in which one of it angles is greater than that angle is an obtuse triangle.^[8] These definitions date back at least to Euclid.^[9]

• 
  Equilateral triangle
 
• 
  Isosceles triangle
 
• 
  Scalene triangle

• 
  Right triangle
 
• 
  Acute triangle
 
• 
  Obtuse triangle