In ΔDAB , m(∡A)=90°=>(Teorema lui Pitagora):DB=√(AD²+AB²)=√(40²+30²)=√(1600+900)=√2500=50
AE⊥BD=>AE->inaltime in ΔDAB
In ΔDAB , m(∡A)=90°=>(a doua teorema a inaltimii):AE*DB=AD*AB=>AE=AD*AB/DB=30*40/50=24
InΔDEA , m(∡E)=90°=>(Teorema lui Pitagora):DE=√(AD²-AE²)=√(30²-24²)=√(900-576)=√324=18
In ΔDCB , m(∡C)=90°=>(a doua teorema a inaltimii):FC*DB=DC*BC=>FC=DC*BC/DB=40*30/50=24
In ΔCFB , m(∡F)=90°=>(Teorema lui Pitagora):FB=√(BC²-FC²)=√(30²-24²)=√(900-576)=√324=18
EF=DB-(DE+EF)=50-(18+18)=50-36=14
EF=14