`#laviken#`
a) Vì $\widehat{xOz}$ và $\widehat{tOy}$ nằm ở vị trí đối đỉnh
$\Rightarrow$ $\widehat{xOz}$`=` $\widehat{tOy}$
Ta có : $\widehat{xOz}$ `+` $\widehat{tOy}$`=120^o`
$\Rightarrow$ `2.` $\widehat{xOz}$`=120^o`
$\Rightarrow$ $\widehat{xOz}$`=120^o/2=60^o`
b) Ta có : $\widehat{xOz}$ `+` $\widehat{xOt}$`=180^o`
$\Rightarrow$ `60^o+` $\widehat{xOt}$`=180^o`
$\Rightarrow$ $\widehat{xOt}$ `=180^o-60^o`
$\Rightarrow$ $\widehat{xOt}$ `=120^o`
