The formula of peach heart in Cartesian two-dimensional coordinate system: r=a( 1-sinθ).

note:

Legend has it that 52-year-old Descartes met 18-year-old Swedish princess Christine. Descartes died after sending the 13 letter to Christine. The letter 13 only contains a short formula: r=a( 1-sinθ).

As soon as the princess saw it, she immediately understood the intention of her lover. She immediately set out to draw a graph of the equation. She was very happy when she saw the figure. She knows that her lover still loves her. It turns out that the graph of the equation is a heart. This is also the famous "heart line".