a/ $\widehat{aOb}$ bù $\widehat{bOc}$
$→\widehat{aOb}+\widehat{bOc}=180^\circ$
mà $\widehat{bOc}=50^\circ$
$→\widehat{aOb}=130^\circ$
b/ $\widehat{aOb}$ phụ $\widehat{bOc}$
$\widehat{bOc}+\widehat{aOb}=90^\circ$
mà $\widehat{bOc}=68^\circ$
$→\widehat{aOb}=22^\circ$