Giải thích các bước giải:
Ta có :
$\widehat{BOC}=180^o-\widehat{OBC}-\widehat{OCB}$
$\to\widehat{BOC}=180^o-(\widehat{ABC}-\widehat{ABO})-(\widehat{ACB}-\widehat{ACO})$
$\to\widehat{BOC}=180^o-\widehat{ABC}+\widehat{ABO}-\widehat{ACB}+\widehat{ACO}$
$\to\widehat{BOC}=(180^o-\widehat{ABC}-\widehat{ACB})+\widehat{ABO}+\widehat{ACO}$
$\to\widehat{BOC}=\widehat{BAC}+\widehat{ABO}+\widehat{ACO}$