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



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.),

∴ =  (axiom. 1.);

and therefore is the equilateral triangle required.

Q.E.D