Euclid:Proposition/I/13

Proposition

In the words of Euclid:

If a straight line set up on a straight line make angles, it will make either two right angles or two angles equal to two right angles.

(The Elements: Book $\text{I}$: Proposition $13$)

Sources

• 1926: Sir Thomas L. Heath: Euclid: The Thirteen Books of The Elements: Volume 1 (2nd ed.) ... (previous) ... (next): Book $\text{I}$. Propositions