[tex]\it \left.\begin{aligned}ABCD-paralelogram \Rightarrow AB||CD\\ \\ E\in AB,\ \ F\in CD\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \end{aligned}\right\} \Rightarrow EB||FD\ \ \ \ \ (1)\\ \\ \\ \left.\begin{aligned}DE\perp AC\\ \\ BF\perp AC\end{aligned}\right\} \Rightarrow DE||BF\ \ \ \ \ (2)\\ \\ \\ (1),\ (2) \Rightarrow BEDF\ -\ paralelogram[/tex]
