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

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.