Answer: Geometry
Descartes was very influential in the field of geometry. In 1637, he published his work La Géométrie as an appendix to Discours de la méthode (Discourse on the Method). This work was the first to propose combining algebra and geometry into a single subject. The result was an algebraic geometry called analytic geometry. This contributed to the ideas of Leibniz and Newton and was important in the development of calculus.
