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Rene Descartes, (1596-1650), French philosopher and mathematician. While travelling in Europe as a young man, Descartes formulated his system of Cartesian coordinates and analytical geometry. This meant that for the first time geometrical problems could be solved algebraically, and vice versa. Descartes' philosophical theories were based on rational knowledge, as he believed that information received through the senses was unreliable. He coined the famous phrase cogito ergo sum ('I think, therefore I am').
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