This is a love story, telling the love story of mathematician Descartes. What you said about drawing love on several axes is actually the story of Descartes and Christine's heart line! Specifically, Descartes wandered to Sweden when the Black Death broke out in continental Europe, met Princess Christine, a small Swedish duchy of 18 years old, and later became her math teacher. Getting along with each other every day makes them fall in love. The princess's father, the king, 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 writes to the princess every day. Because she was intercepted by the king, Christine never received a letter from Descartes. Descartes died after sending the 13 letter to Christine. The letter 13 only contains a short formula: r=a( 1-sinθ). The king couldn't understand that they didn't always talk about love, so he gave this letter to Christine, who had been depressed. As soon as the princess saw it, she immediately understood the intention of her lover. 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. The graph of the equation is a heart. This is also the famous "heart line".

After the king died, Christine ascended the throne and immediately sent people to look for her sweetheart all over Europe. It's a pity that she died and left her alone on earth. ...

It is said that this world-famous alternative love letter is still preserved in the Descartes Memorial Hall in Europe.