therefore EAF, EBF are two triangles having two angles equal to two angles and one side equal to one side, namely EF, which is common to them, and subtends one of the equal angles;
Duo ergo trigona sunt EAZ, EZB duos angulos duobus angulis equales habentia et unum latus uni lateri equale commune ipsorum EZ scilicet subtendens unum equalium angulorum,
Ergo duo anguli ZGE; GEZ trianguli GEZ duobus angulis ZDE; DEZ trianguli ZDE sunt equales. Latus quoque GZ lateri ZD est equale. Latere ergo EZ existente communi
Duorum itaque triangulorum GHZ et HZD duo anguli unius scilicet ZGH et GHZ duobus angulis alterius ZDH et DHZ quisque se respiciens equales. Latus autem duos angulos equales respiciens commune estque ZH.
Quoniam igitur duo anguli AFB, ABF, trianguli ABF, aequales sunt duobus angulis AFD, ADF, trianguli ADF; et latera AB, AD, quae rectis angulis aequalibus opponuntur, aequalia quoque:
Title
Book I
