Bài này e tư vẽ hình nhé:
\[\begin{array}{l}
a)\,\,\,Ta\,\,co:\,\,\,{30^0} < {130^0}\\
\Rightarrow \angle xOy < \angle xOz\\
\Rightarrow Tia\,\,\,Oy\,\,\,nam\,\,\,giua\,\,\,tia\,\,\,Ox,\,\,Oz.\\
\Rightarrow \angle xOy + \angle yOz = \angle xOz\\
\Rightarrow {50^0} + \angle yOz = {130^o}\\
\Rightarrow \angle yOz = {130^0} - {50^0} = {80^0}.\\
b)\,\,Tia\,\,Om\,\,la\,\,phan\,\,giac\,\,cua\,\,\angle yOz\\
\Rightarrow \angle yOm = \angle mOz = \frac{{{{80}^0}}}{2} = {40^0}.\\
Oy\,\,nam\,\,giua\,\,2\,\,tia\,\,Om\,\,\,va\,\,\,Ox\,\,nen\,\,ta\,\,co:\\
\angle xOy + \angle yOm = \angle xOm\\
\Rightarrow \angle xOm = {50^0} + {40^0} = {90^0}.
\end{array}\]