H
E
E
L
E
M
E
N
T
S
AD is equal to AB,
and
AE is half of AD, and AF half of AB,
therefore
AE is equal to AF,
so that
the opposite sides are also equal;
therefore
FG is equal to GE.
Similarly we can prove that
each of the straight lines GH, GK
is equal to
each of the straight lines FG, GE.
