Math Playground
Geometry

3-4-5 triangle

The simplest right triangle in whole numbers — used since ancient Egypt.

The 3-4-5 triangle: sides 3, 4, 5 and a perfect 90° angle. The smallest right triangle in whole numbers.

Builders use it to check square corners — measure 3 along one wall, 4 along the other, and the diagonal is 5 if the corner is true.