Same side exterior angles are supplementary. This means that the sum of their measures is equal to 180 degrees.
To explain further, consider two parallel lines cut by a transversal. The angles formed outside the parallel lines but on the same side of the transversal are what we refer to as same side exterior angles. Since these lines are parallel, the relationships between the angles follow the rules of parallel line geometry.
For example, if one same side exterior angle measures 120 degrees, the other angle will measure 60 degrees. Together, they add up to 180 degrees, confirming that these angles are indeed supplementary. This property is essential in various geometric proofs and calculations.