When the sum of the measures of two angles is 90°, the angles are called complementary angles.
For examples the following pairs are complementary:
(a) 30° and 60°
(b) 45° and 45°
(c) 10° and 80°
When two angles are complementary, each angle is said to be the complement of the other angle. The '10° angle' is complement of the '80° angle'.