Geometry for Elementary School/Polar coordinate system
In the coordinate system we have discussed last chapter, the rectangular/Cartesian coordinate system, the origin is only used to determine how the coordinates are numbered. However, there is another coordinate system where the origin is the very heart and sole of the system. It is called the polar coordinate system. In this chapter, we will discuss the polar coordinate system, and compare it to the rectangular coordinate system.
Basic concepts 
On the right is a typical polar coordinate plane. Nothing is italicised in the diagram because of technical difficulties. The point on the centre is the pole, and is the 'origin' of the polar coordinate system. OX is called the polar axis. OP is the radius vector of P and is usualy represented by a lowercase r.