What do you call the angles that measure 180° together?

Angles that measure 180° together are referred to as supplementary angles. This term is used to describe a pair of angles whose measures add up to 180 degrees. For example, if one angle measures 120 degrees, the other must measure 60 degrees to satisfy the condition of being supplementary. Supplementary angles do not need to be adjacent; they can be separate and still satisfy this criterion, provided their measures add up to 180°.

In contrast, complementary angles are those that add up to 90 degrees. Adjacent angles share a common vertex and a side but may or may not add up to a specific degree. Vertical angles, on the other hand, are formed when two lines intersect, creating two pairs of opposite angles, which are equal in measure but also do not necessarily sum to any particular degree together. Understanding these definitions helps clarify why the angles measuring 180° together are specifically called supplementary angles.