French philosopher and mathematician. His line "I think, therefore I am", 我思故我在, opened modern Western philosophy, and the x-y coordinate system Chinese pupils learn is named after him.
The Cartesian coordinate system is fundamental to high-school mathematics.
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A popular Chinese internet legend has 笛卡儿 send a Swedish princess a love letter holding only r = a(1 − sin θ), whose graph is a heart, the 心形线 'cardioid'. The story is invented: in Sweden he tutored Queen Christina, and died there within months.
