$\text{ a ) Ta có : }$
$\hat{xOz}$ + $\hat{zOy}$ = $\hat{xOy}$
$50^o$ + $\hat{zOy}$ = $100^o$
⇒ $\hat{zOy}$ = $50^o$
$\text{ b) Tia Oz là tia phân giác vì :}$
$\hat{xOz}$ = $\hat{zOy}$ = $50^o$
$\text{ c ) Ta có : }$
$\hat{zOy}$ + $\hat{tOy}$ = $180^o$ ( kề bù )
$50^o$ + $\hat{tOy}$ = $180^o$
⇒ $\hat{tOy}$ = $130^o$