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BOOK I. PROP. XXIII. PROB.
23
T a given point (
) in a given straight line (
), to make an angle equal to a given rectilineal angle (
).
Draw 
between any two points in the legs of the given angle.
Construct 
(pr. 22.).
so that 
= , 
= 
and .
Then 
= (pr. 8.).
Q.E.D.
