Albert Girard

Albert Girard (French pronunciation:

He was the first to use the abbreviations 'sin', 'cos' and 'tan' for the trigonometric functions in a treatise.^[1] Girard was the first to state, in 1625, that each prime of the form 1 mod 4 is the sum of two squares.^[3] (See Fermat's theorem on sums of two squares.) It was said that he was quiet-natured and, unlike most mathematicians, did not keep a journal for his personal life.

In the opinion of Charles Hutton,^[4] Girard was

...the first person who understood the general doctrine of the formation of the coefficients of the powers from the sum of the roots and their products. He was the first who discovered the rules for summing the powers of the roots of any equation.

This had previously been given by

, but Viète did not give these for general roots.

In his paper,

and others.

Girard also showed how the area of a spherical triangle depends on its interior angles. The result is called

References