MATHEMATICIAN

Life
Greek mathematician of the Pythagorean school and contemporary of Archytas, Theodore taught for a period in Athens, where both Plato and Theaethetus were students of his. He is cited by (among others) Xenophon, Plato and Proclus.


Work
Theodore proved that the square roots of the numbers 3, 5, 6, 7, ...17 are incommensurable. While his proof has been lost, it must have been based on geometrical figures. His work was continued by his disciple Theaethetus, and was used by Euclid in his famous "Elements". In the "Theaethetus", Plato presents him explaining Theodore's theories on square roots and incommensurable numbers to Socrates.