H
E
E
L
E
M
E
N
T
S
the four areas AG, MQ, QL, RF are quadruple of AG
and
the four areas CK, KD, GR, RN are quadruple of CK
therefore
the eight areas, which contain the gnomon STU, are quadruple of AK.
Now, since
AK is the rectangle AB, BD, for BK is equal to BD, therefore
four times the rectangle AB, BD is quadruple of AK;
therefore
four times the rectangle AB, BD is equal to the gnomon STU.
