+,Vì \(\widehat{OAz}\)và \(\widehat{OAz'}\)kề bù
\(\Rightarrow\widehat{OAz}\)\(+\widehat{OAz'}\)\(=180^o\)
Mà \(\widehat{OAz}\)\(=30^o\)
\(\Rightarrow\widehat{OAz'}\)\(=180^o-30^o=150^o\)
+,Ta thấy \(\widehat{yOA}\)và \(\widehat{OAz'}\)ở vị trí sole trong
Mà \(\widehat{yOA}\)\(=\widehat{OAz'}\)\(=150^o\)
=> zz'//Oy