Definitions need a grammar check An angle is concave when it has the extensions of its sides. An angle is convex when it doesn't have the extensions of its sides. Two angles are consecutive if they have the vertex and a side in common and they lie on the opposite side as regards the side in common. Two angles are adjacent if the are consecutive and the uncommon sides lie on the same line. Two angles are opposite to the vertex if the sides of the former are the extensions of the latter. The bisector is the ray (half-line? which is better?) which split the angle in two congruent angles. Complementary angles are angles that the sum of their measures is equal to 90º. Supplementary angles are angles that the sum of their measures is equal to 180º.