Geometry Lesson: Triangles

All About Triangles

This page serves as a one-stop reference for triangle lessons, formulas, and defintions which are linked from the rest of this site.

Basic Traits of a Triangle:

  1. A triangle is a polygon with three sides and three angles.

  2. The longest side is the hypotenuse. The other sides are known as legs.

  3. The sum of all three angles is 180 degrees.

  4. An equilateral triangle has three sides that are the same length.

  5. An isosceles triangle has two sides of the same length.

  6. A scalene triangle has three sides that are all different lengths.

Special types of triangles:

  1. 30-60-90 right triangles

  2. 45-45-90 right triangles

  3. 3-4-5 triangle

Related Lessons/Formulas

  1. Pythagorean Theorem

  2. Law of sines

  3. Law of cosines