The two special triangles that are frequently mentioned in Geometry are:

- 45-45-90 triangle
- stands for a triangle with angle measures of 45, 45, and 90 degrees
- side-to-side relationship
- x - x - x times square root of 2

- 30-60-90 triangle
- Stands for a triangle with angle measures of 30, 60, and 90 degrees
- Side-to-Side Relationship
- x - x times square root of 3 - 2x

These triangle are also commonly found in Architecture as well, seeing as these specific triangles are most sturdy out of the others. The following are examples of these triangles in architecture.

The 30-60-90 triangle and the 45-45-90 triangle is found in various structures, from buildings and bridges to skyscrapers and cathedrals.