Adjacent complementary angles: among the four angles formed by the intersection of two straight lines, two angles with a common vertex and a common edge are adjacent complementary angles. Diagonal: Two sides of one angle are relative extension lines of another angle, and two angles like this are diagonal to each other.

Perpendicular: When two straight lines intersect at right angles, they are said to be perpendicular to each other, and one of them is said to be perpendicular to the other. Parallel lines: In the same plane, two disjoint lines are called parallel lines.