Ta có: \(\widehat{AOC}+\widehat{COD}+\widehat{BOD}=180^o\)
Thay \(\widehat{BOD}=\frac{\widehat{AOC}}{2}\)ta có: \(\widehat{AOC}+\widehat{COD}+\frac{\widehat{AOC}}{2}=180^o\)
\(\Rightarrow\widehat{COD}=180^o-\widehat{AOC}-\widehat{\frac{AOC}{2}}\)
Thay số: \(\widehat{COD}=180^o-60^o-\frac{60^o}{2}\)
\(\widehat{COD}=120^o-30^o=90^o\)
\(\Rightarrow OC⊥OD\)