Suppose that a is the inclination of a line perpendicular (or normal) to the line l and p...

Suppose that a is the inclination of a line perpendicular (or normal) to the line l and p is the directed distance of l from the origin, p being positive if l is above the origin and negative if l is below (see Figure 3.21). Show that l can be put into the form

This is called the normal form of the line.

Figure 3.21