Euclid:Proposition/XIV/2/Lemma

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Proposition

In the words of Hypsicles of Alexandria:

If an equilateral and equiangular pentagon be inscribed in a circle, the sum of the squares on the straight line subtending two sides and on the side of the pentagon is five times the square on the radius.

(The Elements: Book $\text{XIV}$: Proposition $2$ : Lemma)


Sources