"La géométrie" by René Descartes is a mathematical work published in 1637 as an appendix to his Discourse on the Method. This groundbreaking text proposes uniting algebra and geometry into a single subject, inventing analytic geometry by reducing geometric shapes to algebraic equations. Descartes introduces algebraic notation still used today and tackles complex problems involving curves and equations. Written deliberately obscurely in French, the work influenced the development of calculus and required later mathematicians to clarify and expand its revolutionary ideas.