In mathematics, two angles are complementary: if the sum of the two angles is 180, then the two angles are complementary, which is called two-angle complementarity. One of the angles is a complement to the other. For example:

∠A = 70, ∠B =10, ∠A+∠ B = 180, saying "∠ A and ∠ B are complementary".

∠C = 130, ∠D = 50, ∠ C+∠ D = 180, saying "∠C and ∠D are complementary".

The following methods are often used to prove the complementarity of the two angles:

According to the definition of complementary angle or adjacent complementary angle

According to the parallelism of two straight lines, the inner angles on the same side are complementary.

According to the diagonal complementation of quadrilateral inscribed in a circle