Euclid:Proposition/III/18

Proposition

In the words of Euclid:

If a straight line touch a circle, and a straight line joined from the center to the point of contact, the straight line so joined will be perpendicular to the tangent.

(The Elements: Book $\text{III}$: Proposition $18$)

Sources

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