Page:First six books of the elements of Euclid 1847 Byrne.djvu/75

Rh QUAL triangles ( and ) on equal bases, and on the same side, are between the same parallels.



If which joins the vertices of triangles be not || , draw ||   (pr. 31.), meeting.

Draw.

Because ||  (const.) = but  =

∴ =, a part equal to the whole, which is absurd.

∴ $$\nparallel$$ : and in the same manner it can be demonstrated, that no other line except  is || : ∴  ||. Q. E. D.