$\Delta ABD, ACE$ đều
$=>DA=BA;AC=AE;\widehat{A_1}=\widehat{A_3}=60^o\\ \widehat{DAC}=\widehat{A_1}+\widehat{A_2}=\widehat{A_3}+\widehat{A_2}=\widehat{BAE}$
Xét $\Delta DAC$ và $\Delta BAE$
$\widehat{DAC}=\widehat{BAE}\\ DA=BA\\ AC=AE\\ \Rightarrow \Delta DAC = \Delta BAE\\ \Rightarrow CD=BE$