[tex]punctele~A~,O~si~C~sunt~coliniare\implies m(\sphericalangle AOC)=180^{\circ}.\\asadar,~ m(\sphericalangle AOC) = \m(\sphericalangle AOB)+ m(\sphericalangle BOC) = 180^{\circ}.~\\(OM = bisectoarea~unghiului~AOB \implies m(\sphericalangle AOM) = m(\sphericalangle MOB) = \frac{72}{2} = 36^{\circ}.\\(ON~este~semidreapta~opusa~lui~(OM \implies m(\sphericalangle MON) = 180^{\circ}.\m(\sphericalangle BOC) = m(\sphericalangle AOC) - m(\sphericalangle AOB) = 180^{\circ} -72^{\circ} = 108^{\circ}.[/tex]
[tex]m(\sphericalangle AON ) + m(\sphericalangle AOM ) = m(\sphericalangle MON )\\m(\sphericalangle AON ) = m(\sphericalangle MON ) - m(\sphericalangle AOM ) \\m(\sphericalangle AON ) = 180^{\circ} - 36^{\circ} = 144^{\circ}[/tex]
