Question

Answer 1

\(a,\widehat{BAC}=\widehat{ACE}\left(=\widehat{ACB}=60\right)\\ \Rightarrow AB//CE\Rightarrow ABCE.là.hình.thang\)

\(b,EC=\dfrac{1}{2}AB=\dfrac{1}{2}AC\left(\Delta ABC.đều\right)\\ \Rightarrow EC=FC\left(=\dfrac{1}{2}AC\right)\\ \Rightarrow\Delta CEF.cân.tại.C\)

Mà \(\widehat{C}=60\Rightarrow\Delta CEF.đều\)

\(c,\widehat{EFC}=\widehat{FCB}\left(=60\right)\\ \Rightarrow EF//BC\Rightarrow EFBC.là.hình.thang\)