Ajutor dau coroana !!!!!!
Vă rog mult !!

ABCD-dreptunghi => m(<B)=90°
In tr ABC:m(<B)=90° => sin(BAC)=BC/AC=>4/5=BC/15=>BC=12.
In tr ABC:m(<B)=90° ==T.P.=>AB²+BC²=AC²=>
AB²+144=225=>AB²=81 =>AB=9