Cho \(\widehat{xOy}\) \(=120^o\). Tia \(Oz\) nằm trong \(\widehat{xOy}\). Tia \(Om\) nằm giữa hai tia \(Ox\) và \(Oz\) sao cho \(\widehat{xOm}=\dfrac{1}{3}\widehat{xOz}\). Tia \(Om\) nằm trong \(\widehat{zOy}\) sao cho \(\widehat{zOn}=\dfrac{2}{3}\widehat{zOy}\).
Vậy \(\widehat{mOn}=\)