H
E
E
L
E
M
E
N
T
S
And, since
BC is equal to CD,
let
CE be subtracted from each;
therefore
the remainder BF is equal to the remainder AD.
But
it is also equiangular with it;
therefore
in BF, AD the sides about the equal angles are reciprocally proportional; [VI.14]
therefore
as FE is to ED,
so is AE to EB
