What defines supplementary angles?

Supplementary angles are specifically defined as two angles whose measures add up to 180 degrees. This characteristic sets them apart from other types of angle pairs. For instance, complementary angles are defined as two angles whose measures total 90 degrees, which is a different concept altogether.

Angles that are congruent refer to angles that have the same measure, but this does not relate to their sum. Similarly, vertical angles are pairs of angles that are opposite each other when two lines intersect, and they are also congruent, but again, this does not pertain to the requirement of the angles summing to 180 degrees.

Thus, the correct definition of supplementary angles is the one that states their sum is 180 degrees, which is critical for understanding various applications in geometry, including properties related to polygons and parallel lines.