Albert Girard

Albert Girard was a French mathematician who lived from 1595 to 1632. He studied at the University of Leiden and made many important contributions to mathematics.

Girard had early thoughts on the fundamental theorem of algebra and gave the inductive definition for the Fibonacci numbers. He was also the first person to use the abbreviations 'sin', 'cos', and 'tan' for the trigonometric functions.

Girard was the first to state in 1625 that each prime of the form 1 mod 4 is the sum of two squares. According to Charles Hutton, Girard was one of the first people to understand how the coefficients of powers are formed from the sum of the roots and their products. This work later helped in the development of group theory by mathematicians like Cauchy and Galois.

In addition to his work in algebra, Girard also showed how the area of a spherical triangle depends on its interior angles. This result is known as Girard's theorem. He was also a lutenist and planned to write a treatise on music, but it was never published.