Equal triangles which are on the same base, and on the same side, are also between the same parallels.Let $ABC$ and $DBC$ be equal triangles which are on the same base $BC$, and on the same side (of it). I say that they are also between the same parallels.For let $AD$ have been joined. I say that $AD$ and $BC$ are parallel. <prf> Thus, $AD$ is parallel to $BC$.Thus, equal triangles which are on the same base, and on the same side, are also between the same parallels.