Giải thích các bước giải:
Cách $1:$
Ta có:
$\widehat{AOB}=180^o-x-\widehat{ABO}$
$\widehat{AOC}=180^o-z-\widehat{CBO}$
$\to \widehat{AOB}+\widehat{AOC}=360^o-(x+z+\widehat{ABO}+\widehat{CBO})$
$\to \widehat{AOB}+\widehat{AOC}=360^o-(x+z+\widehat{ABC})$
$\to \widehat{AOB}+\widehat{AOC}=360^o-(x+z+y)$
$\to x+y+z=360^o-(\widehat{AOB}+\widehat{AOC})$
$\to x+y+z=\widehat{AOC}$
Cách $2:$
Xét $\Delta ABC$ có:
$\widehat{ABC}+\widehat{BCA}+\widehat{CAB}=180^o$
$\to y+(z+\widehat{BCO})+(x+\widehat{OAB})=180^o$
$\to (x+y+z)+(\widehat{BCO}+\widehat{OAB})=180^o$
$\to (x+y+z)=180^o-(\widehat{BCO}+\widehat{OAB})$
$\to (x+y+z)=\widehat{AOC}$
