a) \(\widehat{xOt}\)và \(\widehat{yOt}\)là hai góc kề bù nên :
\(\widehat{yOt}\)= \(180^o-\widehat{xOt}\)= \(180^o-30^o=150^o\)
b) \(\widehat{yOt}\)> \(\widehat{yOt'}\)( \(150^o>60^o\)) nên tia Ot' nằm giữa hai tia Oy và Ot
ta có : \(\widehat{yOt'}+\widehat{tOt'}=\widehat{yOt}\)
hay \(60^o+\widehat{t'Ot}=150^o\)
\(\Rightarrow\widehat{t'Ot}=150^o-60^o=90^o\)