H
E
E
L
E
M
E
N
T
S
let another straight line be so interposed, as FA,
and
let DG be drawn from the point D perpendicular to FA.
Then, since
the angle AGD is right, and the angle DAG is less than a right angle,
AD is greater than DG. [I.19]
But
DH is equal to DA;
therefore
DH is greater than DG,
