a,
$\widehat{xOy} < \widehat{xOz}$ nên Oy nằm giữa Ox, Oz
=> $\widehat{xOy}+ \widehat{yOz}= \widehat{zOx}$
$\Leftrightarrow \widehat{yOz}= 100-60= 40^o$
b,
Ot phân giác $\widehat{yOz}$
=> $\widehat{yOt}= \widehat{zOt}= 0,5\widehat{yOz}= 0,5.40= 20^o$
c,
$\widehat{xOy}+ \widehat{yOt}= \widehat{xOt}$
=> $\widehat{xOt}= 60+20= 80^o$
Ot' là tia đối Ot nên $\widehat{tOt'}= 180^o$
=> $\widehat{xOt'}= \widehat{tOt'} - \widehat{xOt}= 180-80= 180^o$