Analytical process: R = A (1-sin θ) This function has two variables, which can be assigned to A and then solved. The function image is a heart-shaped line. This equation is also called "Cartesian love coordinate formula".

As shown in the figure, the images are a= 1, a=2 and a=3 respectively.

Formula source

When Descartes was in his fifties, the terrible Black Death broke out on the European continent. He was forced to wander to Sweden and became the math teacher of Swedish princess Christine. Getting along day after day makes them fall in love, but the little princess is only 18 years old. When the king knew how they felt, he flew into a rage and ordered Descartes to be executed. Later, she was exiled to France because of her daughter's intercession, and Princess Christine was also under house arrest by her father.

Descartes fell seriously ill soon after he returned to France. He wrote to the princess every day, but he was ruthlessly stopped by the king. Christine never heard from Descartes. Descartes died after sending the thirteenth letter to Christine. This last farewell letter has no language but a short formula: r=a( 1-sinθ).

Seeing this formula, the king felt that they didn't always talk about love, so he was moved by compassion and gave this letter to Christine, who had been unhappy. When the little princess saw it, she immediately understood her lover's intention. She immediately began to draw a diagram of the equation. She was very happy when she saw the chart. She knows that her lover still loves her. It turns out that the coordinate diagram of r=a( 1-sinθ) is a heart, which is the origin of the famous "heart line".