Triangles

Math

Definition

A triangle is a polygon with three sides, three vertices, and three angles that always sum to 180°. Triangles are classified by their sides (equilateral, isosceles, scalene) or by their angles (acute, right, obtuse).

Examples

  • An equilateral triangle has three equal sides and three 60° angles
  • A right triangle has one 90° angle and is used in the Pythagorean theorem
  • Road signs like yield signs are shaped as triangles
Key Fact

The sum of the interior angles of any triangle is always 180°

Related Terms

Pythagorean theorem Triangle congruence postulates Triangle inequality Special right triangles

Study This Concept

Practice triangles with free review games in these units:

Pre-Algebra Unit 9: Area and Perimeter