In the polar coordinates (ρ, θ) of point P, ρ represents the distance from point P to pole zero, and θ represents the included angle between light zero and polar axis.

The relationship between rectangular coordinates and polar coordinates;

The pole is the origin, the polar axis is the X axis, and the rectangular coordinates (x, y) and polar coordinates (ρ, θ) of point P satisfy X = ρ cos θ, and Y = ρ sin θ.

(Drawing a coordinate system is easy to deduce. )

The polar coordinate equation can be derived from the rectangular coordinate equation of a circle:

1, the center of the circle is C(a, 0), and the rectangular coordinate equation of the circle with radius a is (x-a) 2+y 2 = a 2, that is, x 2+y 2 = 2ax, so the polar coordinate equation is ρ = 2acos θ.

2. The rectangular coordinate equation of a circle with the center at the pole and radius r is X 2+Y 2 = R 2, so the polar coordinate equation is ρ = R.