Euclid:Proposition/III/31

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Proposition

In the words of Euclid:

In a given circle the angle in a semicircle is right, that in a greater segment less than a right angle, and that in a less segment greater than a right angle, and further the angle of the greater segment is greater than a right angle, and the angle of the less segment less than a right angle.

(The Elements: Book $\text{III}$: Proposition $31$)


Sources