Orthogonal linesare another way of saying lines are perpendicular—but it is mostly
used in terms of functions, transformations, and vectors in other mathematical fields.
Normal linesare perpendicular lines where each line is perpendicular to a curve
(including a line) or a surface (including a plane). And finally, a line is considered to
be tangentto a circle if it intersects the circle at exactly one point—also called the
176 point of tangency. Such lines are also called tangential lines.
In the above, illustration 1 shows dihedral angle ; illustration 2 shows complementary angles; and illustration 3
shows supplementary angles.