Om là tia phân giác của \(\widehat{xoy}\) nên:
\(\widehat{moy}=\dfrac{\widehat{xoy}}{2}\)
Mà :
\(\widehat{moy}+\widehat{noy}=90^0\)
\(\Rightarrow\dfrac{\stackrel\frown{xoy}}{2}+\widehat{noy}=\dfrac{\widehat{xoz}}{2}\)
\(\Rightarrow\widehat{noy}=\dfrac{\widehat{xoz}-\widehat{xoy}}{2}\)
\(\Rightarrow\widehat{noy}=\dfrac{\widehat{zoy}}{2}\) ( đpcm )