# Mathematician:Albert Girard

## Mathematician

Professional French lutenist who also studied mathematics, working in the fields of algebra, trigonometry and arithmetic.

Gave an inductive formula for the Fibonacci numbers.

First stated in $1632$ that every prime of the form $4 k + 1$ is the sum of two squares in only one way.

Invented the symbol $\sqrt [n] x$ for the $n$th root of $x$.[1]

Also introduced the symbols $\sin$, $\cos$ and $\tan$.

His work led eventually to the creation of group theory.

French

## History

• Born: 1595 in St Mihiel, France.
• Died: 8 Dec 1632 in Leiden, Netherlands.

## Theorems

Results named for Albert Girard can be found here.

## Publications

• 1626: A treatise on trigonometry

(titles unknown)