Giải thích các bước giải:
Theo bài ta có $\dfrac{\widehat{AOC}}{\widehat{BOC}}=\dfrac{4}{5}$
Lại có $\widehat{AOC}+\widehat{BOC}+\widehat{AOB}=360^o\to\widehat{AOC}+\widehat{BOC}=270^o$
$\to\widehat{AOC}=120^o,\widehat{BOC}=150^o$
$\to\widehat{ABC}=\dfrac 12\widehat{AOC}=60^o,\widehat{BAC}=\dfrac 12\widehat{BOC}=75^o,\widehat{ACB}=\dfrac 12\widehat{AOB}=45^o$