H
E
E
L
E
M
E
N
T
S
BE, EC, GL, LH be joined.
Now, since
the polygon ABCDE is similar to the polygon FGHKL, [1.14]
the angle BAE is equal to the angle GFL;
and,
as BA is to AE, so is GF to FL.
Since then
ABE, FGL are two triangles having one angle equal to one angle and the sides about the equal angles proportional,
therefore
the triangle ABE is equiangular with the triangle FGL;
so that it is also similar;
therefore
the angle ABE is equal to the angle FGL.
