# Definition:Euclid's Definitions - Book X (III)

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## Euclid's Definitions: Book $\text{X (III)}$

These definitions appear between Propositions $84$ and $85$ of Book $\text{X}$ of Euclid's *The Elements*.

- Given a rational straight line and an apotome, if the square on the whole be greater than the square on the annex by the square on a straight line commensurable in length with the whole, and the whole be commensurable in length with the rational straight line set out, let the apotome be called a
**first apotome**. - But if the annex be commensurable in length with the rational straight line set out, and the square on the whole be greater than that on the annex by the square on a straight line commensurable in length with the whole, let the apotome be called a
**second apotome**. - But if neither be commensurable in length with the rational straight line set out, and the square on the whole be greater than the square on the annex by the square on a straight line commensurable with the whole, let the apotome be called a
**third apotome**. - Again, if the square on the whole be greater than the square on the annex by the square on a straight line incommensurable with the whole, then, if the whole be commensurable in length with the rational straight line set out, let the apotome be called a
**fourth apotome**; - if the annex be so commensurable, a
**fifth**; - and if neither, a
**sixth**.

## Sources

- 1926: Sir Thomas L. Heath:
*Euclid: The Thirteen Books of The Elements: Volume 3*(2nd ed.) ... (previous) ... (next): Book $\text{X}$. Definitions $\text{III}$