[tex]\it ABCD\ -\ paralelogram\ \Rightarrow\ \begin{cases} \it AB=CD\\ \\ \it BC=AD\end{cases}\\ \\ \\\mathcal{P}=2(AB+BC)=16|_{:2} \Rightarrow AB+BC=8\ \ \ \ (1)\\ \\ Dar,\ \ AB=4\ cm\ \ \ \ \ (2)\\ \\ (1),\ (2) \Rightarrow 4+BC=8 \Rightarrow BC=4\ cm\\ \\ Deci:\ \ ABCD-paralelogram,\ AB=BC \Rightarrow ABCD\ -\ romb[/tex]
(Paralelogramul cu două laturi consecutive congruente este romb.)
