[tex]\it Fie\ \ a=\ lungimea\ unei\ muchii\ laterale\\ \\ AE\perp EC \Rightarrow \Delta EAC-dreptunghic\ isoscel \Rightarrow AC=a\sqrt2\\ \\ ABCD-\ dreptunghi \Rightarrow BD=AC=a\sqrt2\\ \\ \Delta EBD \equiv\Delta EAC\ (LLL) \Rightarrow \Delta EBD-dreptunghic,\ m(\hat E)=90^o \Rightarrow BE\perp ED[/tex]
