Definition:Euclid's Definitions - Book I/21 - Triangles by Angles
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Definition
In the words of Euclid:
- Further, of trilateral figures, a right-angled triangle is that which has a right angle, an obtuse-angled triangle that which has an obtuse angle, and an acute-angled triangle that which has its three angles acute.
(The Elements: Book $\text{I}$: Definition $21$)
Sources
- 1926: Sir Thomas L. Heath: Euclid: The Thirteen Books of The Elements: Volume 1 (2nd ed.) ... (previous) ... (next): Book $\text{I}$. Definitions