Polar coordinate equation is polar coordinate equation. Different from ordinary xy coordinate system, polar coordinate system takes distance (radial direction) and orientation (direction) as fixed points. Actually, it's similar to the trigonometric function you used. The ray passing through point A from the origin is denoted as OA, the angle between OA and the square of polar coordinate axis is α, the length of line segment is r, and the coordinates of point A are (x, y) in xy coordinate system and (r, α) in polar coordinate system.