Chúc bạn học tốt :3

bn zoom ảnh nhé

a) Ta có: $\widehat{xOz}+\widehat{yOz}=\widehat{xOy}$
$\Rightarrow \widehat{yOz}=\widehat{xOy}-\widehat{xOy}=120^{0}-90^{0}=30^{0}$
$\widehat{yOz}+\widehat{tOz}=90^{0}$ (hai góc phụ nhau)
$\Rightarrow \widehat{tOz}=90^{0}-\widehat{yOz}=90^{0}-30^{0}=60^{0}$
b) $\widehat{yOt}+\widehat{xOt}=\widehat{xOy}$
$\Rightarrow \widehat{xOt}=\widehat{xOy}-\widehat{yOt}=120^{0}-90^{0}=30^{0}$
Vì On, Om lần lượt là tia phân giác của $\widehat{yOz}, \widehat{xOt}$
$\Rightarrow \left\{\begin{matrix}
\widehat{nOz}=\frac{\widehat{yOz}}{2}=\frac{30^{0}}{2}=15^{0}\\ 
\widehat{mOt}=\frac{\widehat{xOt}}{2}=\frac{30^{0}}{2}=15^{0}
\end{matrix}\right.$
Ta có: $\widehat{nOz}+\widehat{zOt}+\widehat{mOt}=\widehat{mOn}$
$\Rightarrow \widehat{mOn}=15^{0}+30^{0}+15^{0}=90^{0}$
$\Leftrightarrow Om\perp On$