\(\widehat{O_1}=\widehat{O_4}\left(GT\right);\widehat{O_2}=\widehat{O_3}\left(t/c.phân.giác\right)\\ \Rightarrow\widehat{O_1}+\widehat{O_2}=\widehat{O_3}+\widehat{O_4}\\ \Rightarrow\widehat{yOz}=\widehat{xOz}\)
Mà \(\widehat{yOz}+\widehat{xOz}=\widehat{xOy}=180^0\)
\(\Rightarrow\widehat{yOz}=90^0\Rightarrow Oz\perp xy\)