Descartes, René (1596-1650)
Geometria, à Renato Des Cartes anno 1637 gallicè edita.
Amstelædami : Apud Ludovicum & Danielem Elzevirios, 1659-1661.

Justly famous, Descartes' Geometria introduces a method to solve geometric problems algebraically. Traditionally the product of lines had been considered to be a square but Descartes showed how the product could instead be interpreted as a line by introducing an arbitary unit and using similar triangles. Additionally Descartes solved locus problems that had baffled the ancients.