a,
Ta có: $\widehat{xOy}$=$\widehat{xOz}$
($55^o<110^o$)
=> $Oy$ nằm giữa $Ox;Oz$
b,
$Oy$ nằm giữa $Ox;Oz$
=>$\widehat{xOy}$+$\widehat{yOz}$=$\widehat{xOz}$
=> $55^o$+$\widehat{yOz}$=$110^o$
=> $\widehat{yOz}$=$55^o$
c,
$Oy$ nằm giữa $Ox;Oz$
$\widehat{xOy}$=$\widehat{yOz}$=$55^o$
=> $Oy$ là tia phân giác $\widehat{xOz}$
d,
Ta có:
$\widehat{xOz}$+$\widehat{zOt}$=$\widehat{xOt}$=$180^o$
=> $110^o$+$\widehat{zOt}$=$180^o$
=> $\widehat{zOt}$=$70^o$
