Giải thích các bước giải:
Ta có:
$\widehat{AOC}-\widehat{AOD}=20^o$
$\to \widehat{AOC}=\widehat{AOD}+20^o$
Mà $\widehat{AOC}+\widehat{AOD}=\widehat{COD}=180^o$
$\to (\widehat{AOD}+20^o)+\widehat{AOD}=180^o$
$\to \widehat{AOD}+20^o+\widehat{AOD}=180^o$
$\to 2\widehat{AOD}+20^o=180^o$
$\to2\widehat{AOD}=160^o$
$\to\widehat{AOD}=80^o$
$\to \widehat{AOC}=100^o$
$\to \widehat{DOB}=\widehat{AOC}=100^o$
$\widehat{BOC}=\widehat{AOD}=80^o$