If the sum of two angles is 90 degrees, what type of angles are they?

When two angles add up to 90 degrees, they are classified as complementary angles. The defining characteristic of complementary angles is that their measures sum to 90 degrees, which is a fundamental concept in geometry.

For greater clarity, supplementary angles, which sum to 180 degrees, do not apply here as the requirement is specifically for angles that total 90 degrees. Adjacent angles refer to angles that are next to each other and share a common side but do not necessarily sum to any specific value. Congruent angles are angles that have the same measure but again do not relate directly to the sum being 90 degrees. Thus, the only fitting classification for the situation described is complementary angles.