Giải:
Ta có: AB//CD \(\Rightarrow\widehat{AEE'}=\widehat{CE'N}\)
\(\Rightarrow\widehat{AEx}=\widehat{xEE'}=\widehat{CE'y}=\widehat{NE'y}=\dfrac{1}{2}\widehat{AEE'}=\dfrac{1}{2}\widehat{AE'E}\)
\(\Rightarrow\widehat{xEE'}=\widehat{yE'N}\) (2 góc đồng vị)
\(\Rightarrow\) Ex // E'y