Răspuns:
[tex]AB\parallel CD[/tex]
Din teorema lui Thales avem [tex]\frac{OD}{OB}=\frac{OC}{OA}[/tex]
[tex]\frac{OC}{OA}=\frac{3}{5} \\ \\ \frac{OC}{AC}=\frac{OC}{OA+OC}=\frac{3}{5+3}=\frac{3}{8} \\ \\ OC=\frac{3}{8}\times AC=\frac{3}{8}\times 48=18~cm \\ \\ OA=48-18=30~cm[/tex]
