Câu 1.
a) Các góc kề với $\widehat{xOy}$ là: $\widehat{yOz}$ ; $\widehat{yOt}$
b)
$\widehat{xOy}+\widehat{yOz}+\widehat{zOt}=\widehat{xOt}$
$\Rightarrow {{20}^{o}}+\widehat{yOz}+\widehat{zOt}={{90}^{o}}$
Vì $\widehat{yOz}=\widehat{zOt}$
$\Rightarrow 2.\widehat{zOt}={{90}^{o}}-{{20}^{o}}={{70}^{o}}$
$\widehat{zOt}={{70}^{o}}:2={{35}^{o}}$