a) Do $\widehat{xOy}$ và $\widehat{yOz }$ là hai góc kề bù
⇒$\widehat{xOy}+$$\widehat{yOz}=$`180^0`
`⇒70^0+`$\widehat{yOz}=$`180^0`
`⇒`$\widehat{yOz}=$`180^0-70^0`
`⇒`$\widehat{yOz}=$`110^0`
b)Có $\widehat{xOt}+$$\widehat{yOt}=$`70^0`
`⇒40^0+`$\widehat{yOt}=$`70^0`
`⇒`$\widehat{yOt}=$`70^0-40^0`
`⇒`$\widehat{yOt}=$`30^0`