Đáp án:
$\begin{array}{l}
a)AM = MB = \dfrac{1}{2}AB = 4\left( {cm} \right)\\
b)Trong:\Delta AOM \bot M\\
\Rightarrow \sin \widehat {OAM} = \dfrac{{OM}}{{OA}} = \dfrac{3}{5}\\
\Rightarrow \widehat {OAM} = {37^0}\\
\Rightarrow \widehat {AOM} = {90^0} - \widehat {OAM} = {53^0}\\
Do:\Delta AOM = \Delta BOM\left( {c - c - c} \right)\\
\Rightarrow \widehat {AOM} = \widehat {BOM}\\
\Rightarrow \widehat {AOB} = 2.\widehat {AOM} = {106^0}
\end{array}$
