1650 In Stockholm, 52-year-old mathematician Descartes met 18-year-old Swedish princess Christine. Descartes was so poor that he didn't want to beg from others. He just studied math problems with a broken pen and paper every day. One day, Christine's carriage passed by the street and found Descartes studying mathematics. The princess got off and asked. Finally, Descartes found that the princess was very talented in mathematics. A few days after his farewell, Descartes was told that the king wanted him to be Princess Christina's math teacher. Descartes and Christine fell in love in the next few years. The king found and killed Descartes. In Descartes' last love letter to Christine, the mathematical coordinate equation of r=a( 1-sinθ) appeared, and it was solved into a heart-shaped pattern, which is the famous "heart-shaped line". This love letter was finally collected in the Descartes Museum in Europe.
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