a: \(\widehat{tOa}=\dfrac{\widehat{xOt}}{2}\)
\(\widehat{tOb}=\dfrac{\widehat{yOt}}{2}\)
Do đó: \(\widehat{tOa}+\widehat{tOb}=\dfrac{1}{2}\left(\widehat{xOt}+\widehat{yOt}\right)=\dfrac{1}{2}\cdot180^0\)
hay \(\widehat{aOb}=90^0\)
b: \(\widehat{aOb}=\widehat{tOa}+\widehat{tOb}=\dfrac{1}{2}\left(\widehat{xOt}+\widehat{yOt}\right)=\dfrac{1}{2}\widehat{xOy}\)