Đáp án:
a)$\widehat{MON}=20^{\circ}$
b)
$\widehat{BON}=\widehat{MOA}=90^{\circ}$
Giải thích các bước giải:
a)Vì $OM\perp OA\Rightarrow \widehat{MOA}=90^{\circ}$
$\Rightarrow \widehat{BOM}=\widehat{AOB}-\widehat{MOA}=160^{\circ}-90^{\circ}=70^{\circ}$
$\Rightarrow \widehat{MON}=\widehat{BON}-\widehat{BOM}=90^{\circ}-70^{\circ}=20^{\circ}$
b)
$\widehat{BON}=\widehat{MOA}=90^{\circ}$