H
E
E
L
E
M
E
N
T
S
let FG be drawn from F perpendicular to DE.
Then, since
the angle FGC is right,
the angle FCG is acute; [I.17]
and the greater angle is subtended by the greater side; [I.19]
therefore
FC is greater than FG.
But
FB is equal to FC;
therefore
FB is also greater than FG,
