# Mathematician:Albert Girard

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## 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.

## Nationality

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

- 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)

## Sources

- 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 - 2008: David Nelson:
*The Penguin Dictionary of Mathematics*(4th ed.) ... (previous) ... (next): Entry:**Girard, Albert**(1595-1632)

## References

- ↑ See Earliest Uses of Symbols of Operation in Jeff Miller's website Earliest Uses of Various Mathematical Symbols.