a) $\widehat{kOa}+\widehat{aOi}=180^o$ (kề bù)
$⇒ \widehat{aOi}=180^o-\widehat{kOa}=180^o-120^o=60^o$
$\widehat{bOi}+\widehat{kOb}=180^o$ (kề bù)
$⇒ \widehat{kOb}=180^o-\widehat{bOi}=180^o-60^o=120^o$
b) $\widehat{aOk}+\widehat{kOb}+\widehat{aOb}=360^o$
$⇒ \widehat{aOb}=360^o-\widehat{aOk}+\widehat{kOb}=360^o-240^o=120^o$
$⇒ \widehat{aOk}=\widehat{kOb}=\widehat{aOb}=120^o$