[tex]\it \Delta{ D EF} \sim \Delta EFD \Rightarrow\begin{cases}\it \hat D=\hat E\\ \\ \it \hat E=\hat F\\ \\ \it \hat F=\hat D\end{cases} \Rightarrow \it \hat D=\hat E=\it \hat F \Rightarrow \Delta D EF- echilateral \Rightarrow\\ \\ \\ \Rightarrow \hat D=\hat E=\it \hat F=60^o[/tex]
