[tex]\it Vom\ nota\ AB=a,\ \ BC=b.\\ \\ \mathcal{P}=2(a+b)=84|_{:2} \Rightarrow a+b=42\ \ \ \ \ \ (1)\\ \\ \{a,\ b\}\ d.\ p.\ \{6,\ 8\} \Rightarrow \dfrac{a}{6}= \dfrac{b}{8}= \dfrac{a+b}{6+8}\ \stackrel{(1)}{=}\ \dfrac{42}{14}=3\ \ \ \ \ (2) \\ \\ (2) \Rightarrow \begin{cases} \it \dfrac{a}{6}=3 \Rightarrow a=6\cdot3 \Rightarrow a=18\\ \\ \\ \it \dfrac{b}{8}=3 \Rightarrow b=8\cdot3 \Rightarrow b=24\end{cases}\\ \\ \\ Deci,\ \ AB=CD=18\ cm,\ \ BC=AD=24\ cm[/tex]
