Two Angles are Complementary if they add up to 90 degrees.
In a triangle with a right
angle the other two angles are complementary: angle A + angle
C = 90°. If the two complementary angles are adjacent (i.e.
have a common vertex and share a side, but do not have any
interior points in common) their non-shared sides form a right
In Euclidean geometry, the two acute angles in a right triangle
are complementary, because there are 180° in a triangle
and 90° have been accounted for by the right angle.