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 $x$.

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

His work led eventually to the creation of group theory.

Nationality

French

History

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

Theorems

• Girard's Theorem
• Newton-Girard Formulas (with Isaac Newton)

Results named for Albert Girard can be found here.

Publications

• 1625: A French translation of the works of Simon Stevin

• 1625: A French translation of Books $\text V$ and $\text {VI}$ of Diophantus's Arithmetica (the Wilhelm Xylander edition)

• 1626: A treatise on trigonometry

(titles unknown)

• 1629: Invention Nouvelle en l'Algèbre

Sources

• John J. O'Connor and Edmund F. Robertson: "Albert Girard": MacTutor History of Mathematics archive

• 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): A List of Mathematicians in Chronological Sequence
• 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): A List of Mathematicians in Chronological Sequence
• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): Girard, Albert (1595-1632)
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): Girard, Albert (1595-1632)