DE/EC=3 aplic propietatile de la proportii derivate
(DE+EC)/EC=3+1/1
DC/EC=4/1
DC=4EC
in ΔFAB aplic T. Thales FC/FB=EC/AB=EC/AB=1/4
FC/FB=1/4 apoi proportii derivate
FC/(FB-FC)=1/(4-1)
FC/15=1/3 FC=15/3=5 cm FB=15+5=20
-in ΔFAB, dreptunghic, aplic sin(FAB)=FB/AF
dar AF²=AB²+FB²=400+(15+5)²=2*400
AF=20√2
sin(FAB)=FB/AF=20/20√2=√2/2
Desenul il poti face foarte simplu dupa indicatiile enuntului. Nu-l pot face acum!!!
