Albert Girard was French but went as a religious refugee to the Netherlands. He attended the University of Leiden, where he studied mathematics, entering the University at the age of 22. In fact his first interest was music and he played the lute professionally.
Albert Girard worked on algebra, trigonometry and arithmetic. In 1626 he published a treatise on trigonometry containing the first use of the abbreviations sin, cos, tan. He also gave formulae for the area of a spherical triangle.
In algebra he had some early thoughts on the fundamental theorem of algebra and translated the works of Stevin in 1625. He is also famed for being the first to formulate the (now well known) inductive definition fn+2 = fn+1 + fn for the Fibonacci sequence.
Like many mathematicians of his day Albert Girard was interested in military applications of mathematics and in particular studied fortifications. He translated several works on fortifications some from French to Flemish, others from Flemish to French.
It appears that Girard spent some time as an engineer in the Dutch army although this was probably after he published his work on trigonometry. Gassendi, writing to a friend, talks about Girard and refers to his position in the Dutch army. He was described as an engineer rather than as a mathematician on his death.
Article by: J J O'Connor and E F Robertson
December 1996