[tex]\it\ell < L\ cu\ 14 \Rightarrow \ell=L-14\ \ \ \ \ (1)\\ \\ \mathcal{A}=L\cdot \ell=1800\ \stackrel{(1)}{\Longrightarrow}\ L(L-14)=1800 \Rightarrow L^2-14L=1800\bigg|_{+49} \Rightarrow \\ \\ \\ \Rightarrow L^2-14L+49=1849 \Rightarrow (L-7)^2=43^2 \Rightarrow L-7=43\bigg|_{+7\ m} \Rightarrow L=50\ m\\ \\ \\ \ell=L-14=50-14=36\ m[/tex]
