The four-leaf rose line is a line segment in mathematical concept, and its polar coordinate equation is P=asin2θ.

A definition of the four-leaf line: a fixed-length line segment AB=2a, with two endpoints sliding on two vertical lines. The line segment AB is taken as the vertical line OM from the intersection o of the two lines, and the trajectory of the vertical foot M is called the four-leaf rose line (see figure). Its polar coordinate equation is P=asin2θ.