# Diophantus

**Diophantus of Alexandria** - Διόφαντος ο Αλεξανδρεύς - (circa 200/214 – circa 284/298) was a Greek mathematician.
He was known for his study of equations with variables which take on rational values and these Diophantine equations are named after him. Diophantus is sometimes known as the "father of Algebra". He wrote a total of thirteen books on these equations. Diophantus also wrote a treatise on polygonal numbers.

In 1637, while reviewing his translated copy of Diophantus' *Arithmetica* (pub. ca.250) Pierre de Fermat wrote his famous "Last Theorem" in the page's margins. His copy with his margin-notes survives to this day.

Although little is known about his life, some biographical information can be computed from his epitaph (see links below). He lived in Alexandria and he died when he was 84 years old. Diophantus was probably a Hellenized Babylonian.

A 5th and 6th century math puzzle involving Diophantus' age: He was a boy for one-sixth of his life. After one-twelth more, he acquired a beard. After another one-seventh, he married. In the fifty year after his marriage his son was born. The son lived half as many as his father. Diophantus died 4 years after his son. How old was Diophantus when he died?

The answer: 84 The answer is determined from two methods: 1. Finding the common multiple of 12, 6, and 7 (which is 84). 2. Taking 14 (the age up to which would be considered a boy; one-sixth of his life) multiplied by 6, which equals 84.

## External links

- Diophantus of Alexandria by J. J. O'Connor and E. F. Robertson
- Diophantus's Riddle Diophantus' epitaph, by E. Weisstein
- Larry Freeman (2005), Fermat's Last Theorem Blog Covers topics in the history of Fermat's Last Theorem from Diophantus of Alexandria to Andrew Wiles.

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