|Book III Proposition 20|
let AE be joined and drawn through to F.
EA is equal to EB,
the angle EAB is also equal to the angle EBA; [I.5]
the angles EAB, EBA are double of the angle EAB.
the angle BEF is equal to the angles EAB, EBA; [I.32]
the angle BEF is also double of the angle EAB.
|Previous Page Return to Propositions Next Page|