Then, since CB, BG, GH are equal to one another,
the triangles ABC, AGB, AHG are also equal to one another. [I. 38]
Therefore, whatever multiple the base HC is of the base BC,
that multiple also is the triangle AHC of the triangle ABC.
For the same reason, whatever multiple the base LC is of the base CD, that multiple also is the triangle ALC of the triangle ACD;
and, if the base HC is equal to the base CL, the triangle AHC is also equal to the triangle ACL, [I. 38]
if the base HC is in excess of the base CL,
the triangle AHC is also in excess of the triangle ACL, and, if less, less.
Thus, there being four magnitudes, two bases BC, CD and two triangles ABC, ACD,
equimultiples have been taken of the base BC and the triangle ABC, namely the base HC and the triangle AHC,
and of the base CD and the triangle ADC other, chance, equimultiples, namely the base LC and the triangle ALC;
and it has been proved that, if the base HC is in excess of the base CL,
the triangle AHC is also in excess of the triangle ALC;
if equal, equal; and, if less, less.
Therefore, as the base BC is to the base CD, so is the triangle ABC to the triangle ACD. [V. Def. 5]