\(\text{a) Vì 2 góc }\widehat{xOy}\text{ và }\widehat{yOz}\text{ là 2 góc kề bù}\)
\(\Rightarrow\widehat{xOy}+\widehat{yOz}=180^0\)
\(\text{hay }\widehat{xOy}+50^0=180^0\)
\(\widehat{xOy}=180^0-50^0\)
\(\widehat{xOy}=130^0\)
\(\text{b) Vì tia Ot nằm giữa 2 tia Ox và Oy}\)
\(\Rightarrow\widehat{xOt}+\widehat{tOy}=\widehat{xOy}\)
\(\text{hay }20^0+\widehat{tOy}=130^0\)
\(\widehat{tOy}=130^0-20^0\)
\(\widehat{tOy}=110^0\)