# Mathematician:Theaetetus of Athens

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## Mathematician

Greek mathematician whose principal contribution was the material on irrational lengths, included in Book $\text X$ of Euclid's *The Elements*.

Also proved that there are precisely five regular convex polyhedra.

All we know about him was what Plato (who rated him highly) wrote about him.

## Nationality

Greek

## History

- Born: about 417 BCE in Athens, Greece
- Died: about 369 BCE in Athens, Greece

## Theorems and Definitions

- Five Platonic Solids
- Much if not all of the content of Book $\text X$ of Euclid's
*The Elements*

## Sources

- John J. O'Connor and Edmund F. Robertson: "Theaetetus of Athens": 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):**Theaetetus**(*c*. 414-*c*. 369 bc) - 2008: David Nelson:
*The Penguin Dictionary of Mathematics*(4th ed.) ... (previous) ... (next):**Theaetetus**(*c*. 414-*c*. 369 bc)