This page has been validated.
16
BOOK I. PROP. XVI. THEOR.
F a side of a triangle (
) is produced, the external angle (
) is greater than either of the internal remote angles (
or 
).
Make 
= 
(pr. 10.).
Draw 
and produce it until 
= ; draw 
.
In 
and 
; = 
= 
and = (const. pr. 15),
∴ 
= (pr. 4.),
∴ >
In like manner it can be shown, that if 
be produced, 
> , and therefore
which is = is > .
Q.E.D.
