When the sum of the measures of two angles is 180°, the angles are called supplementary angles.
For examples the following pairs are complementary:
(a) 30° and 150°
(b) 145° and 35°
(c) 100° and 80°
When two angles are complementary, each angle is said to be the supplement of the other angle. The '100° angle' is supplement of the '80° angle'.