Vì $\widehat{AOM}-\widehat{BOM}=40^o$
$→\widehat{AOM}=40^o+\widehat{BOM}$
mà $\widehat{AOM}+\widehat{BOM}=180^o$
$→40^o+\widehat{BOM}+\widehat{BOM}=180^o$
$→2.\widehat{BOM}=140^o$
$→\widehat{BOM}=\dfrac{140^o}{2}=70^o$
$→\widehat{AOM}=40^o+70^o=110^o$
Vì $AB∩MN≡O$
$→\widehat{AOM}=\widehat{BON}=110^o$ (đối đỉnh)
$→\widehat{BOM}=\widehat{AON}=70^o$ (đối đỉnh)
Vậy $\widehat{AOM}=\widehat{BON}=110^o$
$\widehat{BOM}=\widehat{AON}=70^o$