2. Let a point o be the pole on the plane. Starting from o, draw a ray Ox, which is called the polar axis. Take another unit length, usually specifying that the counterclockwise direction is positive. The position of any point P on the plane can be determined by the length ρ of the line segment OP and the included angle θ between Ox and OP, and the ordered number pair (ρ, θ) is called the polar coordinates of the point P; ρ is called the polar diameter of point P, and θ is called the polar angle of point P. ..