What term describes two angles that add up to 90 degrees?

Two angles that add up to 90 degrees are referred to as complementary angles. This relationship is fundamental in geometry, particularly in the study of angles. When two angles are complementary, their measures combine to form a right angle, which is a pivotal concept in various geometric constructions and proofs.

Understanding complementary angles is essential because they commonly appear in right triangle problems, where one angle is often a complement of another. For instance, in a right triangle, the two non-right angles are always complementary, meaning they will always add up to 90 degrees, which is foundational in trigonometry as well.

The other terms provided describe different relationships: straight angles combine to form 180 degrees, supplementary angles also add up to 180 degrees, and adjacent angles share a common side and vertex but do not necessarily add up to any specific angle measure. Recognizing the specific definitions and relationships between these terms is crucial for mastering geometry.