Who was Theodorus of Cyrene?

Theodorus of Cyrene was a 5th-century BC ancient Greek mathematician known primarily through the surviving dialogues of Plato. He explored the theory of incommensurable quantities and is credited with proving the irrationality of square roots up to 17. He also served as a teacher to notable figures such as Plato and Theaetetus.

What we know

• Theodorus of Cyrene was an ancient Greek mathematician who flourished around 450 BC. [1, 2]
• The only surviving first-hand accounts of Theodorus are found in three of Plato's dialogues: the Theaetetus, the Sophist, and the Statesman. [2]
• Theodorus advanced a proof for the irrationality of square roots from 3 up to 17. [2]
• Both Plato and the mathematician Theaetetus were students of Theodorus of Cyrene. [3]

Where to go next

• how it workedWhat was the Spiral of Theodorus?
• how we knowHow did Plato influence mathematics?
• whereWhat was ancient Cyrene like?
• whoWho was the mathematician Theaetetus?
• the bigger pictureWhat is Euclid's Book X about?
• an unexpected connectionHow does a lunar crater connect to an ancient mathematician?Theaetetus, a student of Theodorus of Cyrene, is commemorated with a crater named Theaetetus on the Moon.

Sources

• [1]Theodoros of Cyrene (Wikidata Q712328) · CC0 1.0
• [2]Theodorus of Cyrene · CC BY-SA 4.0
• [3]Theaetetus (mathematician) · CC BY-SA 4.0
• [4]Cyrene, Libya · CC BY-SA 4.0
• [5]List of ancient Greeks · CC BY-SA 4.0