Page:First six books of the elements of Euclid 1847 Byrne.djvu/44

10 O bisect a given finite straight line.

Construct (pr. 1.), draw, making  =  (pr. 9.).

Then =  by (pr. 4.), for  =  (const.)  =  and  common to the two triangles. Therefore the given line is bisected. Q.E.D.