$\text{Trên cùng một nửa mặt phẳng bờ chứa tia Ox có:}$
$\text{$\widehat{xOz}$ = $40^{o}$; $\widehat{xOy}$ = $110^{o}$ (gt)}$
$\text{⇒ $\widehat{xOz}$ < $\widehat{xOy}$}$
$\text{⇒ Tia Oz nằm giữa Ox và Oy}$
$\text{⇒ $\widehat{xOz}$ + $\widehat{yOz}$ = $\widehat{xOy}$}$
$\text{⇒ $\widehat{yOz}$ = $\widehat{xOy}$ - $\widehat{xOz}$}$
$\text{⇒ $\widehat{yOz}$ = $110^{o}$ - $40^{o}$}$
$\text{⇒ $\widehat{yOz}$ = $70^{o}$}$
$\text{Có: Ot là tia p/g của $\widehat{yOz}$ (gt)}$
$\text{⇒ $\widehat{zOt}$ = $\widehat{yOt}$ = $\dfrac{\widehat{yOz}}{2}$ = $\dfrac{70^o}{2}$ = $35^{o}$}$
$\text{Có: $\widehat{xOt}$ = $\widehat{xOz}$ + $\widehat{zOt}$}$
$\text{⇒ $\widehat{xOt}$ = $40^{o}$ + $35^{o}$}$
$\text{⇒ $\widehat{xOt}$ = $75^{o}$}$
