When two straight lines intersect, two corners with a common vertex and a common edge or two corners have a common edge, and the other side of the two corners is an opposite extension line. A corner has two adjacent complementary angles. The sum of an angle and its adjacent complementary angles is equal to 180. "Adjacent complementary angles" includes two requirements: the positional relationship and the quantitative relationship between two angles. The complementary angle is only the quantitative relationship between two angles.