[tex]P=20~cm=4l=\ \textgreater \ l=5~cm \\ AC~intersectat~cu~BD=O \\ DO=OB=3~cm \\ \left \{ {{tr.~AOB} \atop {m(\ \textless \ O)=90~grade}} \right.=\ \textgreater \ AO^2+OB^2=AB^2 \\ AO^2+9=25 \\ AO^2=16 \\ AO=4 \\ AO=OC=\ \textgreater \ AC=8~cm \\ A_A_B_C_D= \frac{DB*AC}{2}= \frac{6*8}{2}=24~cm^2 [/tex]
