ae=ab-be=24-15=9
Aplicam reciproca teor. Thales=> ae/ab=af/ac => 9/24=12/36=>3/8=3/8 si este adevarat=> ef paralel cu bc..
Apoi pt a afla ef aplicam teorema fundamentala a asemanarii in abc => ae/eb = af/fc= ef/bc.. luam doar ae/eb=ef/bc => ef= (ae ×bc)/eb => ef = (9×36)/15