a, Vì \(\widehat{xOy}\)là góc bẹt \(\Rightarrow\widehat{xOy}\)\(=180^o\)
Trên cùng một nửa mặt phẳng bờ chứa tia Oy, có:
\(\widehat{zOy}\)<\(\widehat{xOy}\) ( vì 60\(^o\)<\(180^o\))
\(\Rightarrow\) Tia Oz nằm giữa 2 tia Ox, Oy
\(\Rightarrow\)\(\widehat{zOy}\)\(+\widehat{xOz}\)\(=\widehat{xOz}\)
\(\Rightarrow\) \(60^o+\widehat{xOz}\)\(=180^o\)
\(\widehat{xOz}\)\(=180^o-60^o\)
\(\widehat{xOz}\)\(=120^o\)
b, Mink chịu