[tex3]
\angle ADC=\alpha,\,\angle BAD=\beta\\
CD=BF,DE=CB,\angle EDC=\angle CBF \implies \triangle CBF \underset{LAL }{\equiv}\triangle CDE\implies CE=CF\\
\angle EAF=2\pi-\frac{2\pi}{3}-\beta=\frac{4\pi}{3}-\beta=\frac{4\pi}{3}-\pi+\alpha=\frac{\pi}{3}+\alpha=\angle EDC\\
\angle EAF=\angle EDC,DE=AE,DC=AF\implies\triangle AFE\underset{LAL}{\equiv} \triangle CDE\implies FE=CE\\
CE=FE=CF\implies \triangle EFC\text{ equilátero}[/tex3]...