Albert Girard

Albert Girard was a French mathematician and musician of the early seventeenth century who lived most of his working life in the Dutch Republic, having gone there as a religious refugee from France because he belonged to the Reformed church. He studied mathematics at the University of Leiden, where he discussed scientific questions with Jacob Golius, and he later served as an engineer in the army of the Prince of Orange. His 1626 work on trigonometry is the first to use the abbreviations sin, cos and tan, and it also gave a formula for the area of a spherical triangle. In his 1629 Invention Nouvelle en l'Algebre he related the coefficients of an equation to the sums and products of its roots, stated that an equation of degree four has four roots, real or imaginary, and gave an early geometric reading of negative quantities. He also edited and extended the mathematical works of Simon Stevin, which appeared in 1634 after Girard died in Leiden in 1632.