Page:First six books of the elements of Euclid 1847 Byrne.djvu/35

Euclid.

BOOK I.

PROPOSITION I. PROBLEM.

N a given finite ſtraight line () to deſcribe an equilateral triangle.

Deſcribe and (poſtulate 3.); draw and (poſt. 1.).

then will be equilateral.

For $=$ (def. 15.);

and $=$ (def. 15.),

$\therefore$ $=$ (axiom. 1.);

and therefore is the equilateral triangle required.

Q.E.D.