Equal triangles which are on equal bases, and on the same side, are also between the same parallels. * Let $ABC$ and $CDE$ be equal triangles on the equal bases $BC$ and $CE$ (respectively), and on the same side (of $BE$). * I say that they are also between the same parallels.
Triangles which are equal in area (\(\triangle{ABC}=\triangle{DCE}\)) as well as stand on equal bases (\(\overline{BC}\), \(\overline{CE}\)) and on the same side of their bases stand on the same parallels (\(\overline{AD}\parallel\overline{BE}\)).
Proofs: 1
This whole proposition is regarded by Heiberg as a relatively early interpolation to the original text (translator's note). ↩