Yes, if the exterior sides of two adjacent angles are opposite rays, then the angles are supplementary.
To explain this, let’s break down the terms: adjacent angles are two angles that share a common vertex and a common side but do not overlap. If the exterior sides of these adjacent angles are opposite rays, it means that when you extend those sides, they go in opposite directions, essentially forming a straight line.
A straight line measures 180 degrees. Therefore, the sum of the measures of these two angles will also equal 180 degrees. This is the defining property of supplementary angles. So in this case, when the exterior sides of the angles are opposite rays, it directly leads to the conclusion that these angles are indeed supplementary.