When I was still studying in senior high, my mathematics teacher told us a love story about the French mathematician René Descartes and a Swedish Princess Kristina.

By the year 1648, when the princess is 18, Descartes was appointed to be the teacher of the young princess. Descartes taught her Cartesian coordinates system(直角坐標系), and soon they fell in love with each other. The King was furious when he learnt that his daughter was in love, and he expelled Descartes out from Sweden.

On one hand, Descartes soon felt into a serious illness, the Black Death, and could hardly recover since then. During his illness, he wrote 12 letters to Kristina, but there was no reply. Descartes died after he wrote the 13th letter to Kristina.

On the other hand, the King intercepted the letters from Descartes, and never gave them to Princess Kristina. Yet the King found the 13th letter, which only the math equation "r=a(1-sinΘ)" was written, difficult to understand. Therefore, he finally gave this letter to Kristina, hoping the letter might cheer her up a bit. At last, Princess Kristina solve the maze, and found out that Descartes was actually confessing his true heart to her.

Isn't this story beautiful? Yet we have to remember this in mind: story is often only a romantic fantasy.

In the Swedish history, by the year 1648 was the Swedish Kingdom ruled by Drottning Kristina (Queen Kristina). Though Descartes actually visited Sweden by the time, he discuss philosophy instead of mathematics. In February, 1650, Descartes contracted pneumonia(肺炎) in Sweden, and died after ten days.

Resources: Baidu Baike (百度百科)