The Compendium Geometry is an eBook providing facts, formulas and explanations about geometry.

Congruent and Similar Triangles

Congruent Triangles

For congruent triangles there are special rules. Two triangles are congruent if

  • the three sides are equal, or
  • two sides and the common angle are equal, or
  • two sides and the angle opposite the longer side are equal, or
  • one side and two angles are equal.
Please note that triangles with three equal angles are not necessarily congruent (since the sum of angles is always 180, regardless of the length of the sides).


Similar Triangles

Two triangles are said to be similar if

  • the angles of each triangle are equal, or
  • the ratio between the three sides are equal, or
  • one angle and the ratio between two sides is equal.

Last Update: 2010-12-06