To uniquely define a triangle, we need to determine three measurements, at least one of which is a side. Since one of the angles of a right triangle is 90°, we only need to know two more measurements in order to find the remaining unknowns. Knowing how to solve a right triangle will help us build a good foundation for working with any type of triangle.

If one of the two additional measurements is a side and the other is an angle, trigonometric relationships (sin, cos, tan, etc.) can be applied to find the missing parts. When both of the additional measurements are sides, the Pythagorean Theorem can be used to calculate the missing side. Then, the two missing angles can be found by using trigonometric relationships.