PROPOSITION 93.
If an area be contained by a rational straight line and a third apotome, the “side”
of the area is a second apotome of a medial straight line.
For let the area
AB be contained by the rational straight line
AC and the third apotome
AD; I say that the “side”
of the area
AB is a second apotome of a medial straight line.
For let
DG be the annex to
AD; therefore
AG,
GD are rational straight lines commensurable in square only, and neither of the straight lines
AG,
GD is commensurable in length with the rational straight line
AC set out, while the square on the whole
AG is greater than the square on the annex
DG by the square on a straight line commensurable with
AG. [
X. Deff. III. 3]
Since then the square on
AG is greater than the square on
GD by the square on a straight line commensurable with
AG, therefore, if there be applied to
AG a parallelogram equal to the fourth part of the square on
DG and deficient by a square figure, it will divide it into commensurable parts. [
X. 17]
Let then
DG be bisected at
E, let there be applied to
AG a parallelogram equal to the square on
EG and deficient by a square figure, and let it be the rectangle
AF,
FG.