A (dreptunghiului)=L × l unde L= l+2cm
48 = (l+2cm) × l ⇔ l² + 2l -48 =0 , Δ = 2² - 4*1*(-48) = 4+192=196
√Δ = 14 ;
[tex]l_{1;2}=\frac{-2\pm14}{2}\;\rightarrow\;l_1=6\;si\;l_2=\,-8(fiind\,negativ\,nu\,ne\,convine!)\\
P_{dreptunghiului}=2\cdot(L+l)=2\cdot[(6+2)+6]=28\,cm[/tex]