\(a,\widehat{O_1}=\widehat{O_4};\widehat{O_2}=\widehat{O_3}\left(giả.thiết\right)\\ \Rightarrow\widehat{O_1}+\widehat{O_2}=\widehat{O_3}+\widehat{O_4}\\ \Rightarrow\widehat{AOC}=\widehat{AOB}\)
Mà \(\widehat{AOC}+\widehat{AOB}=\widehat{AOB}=180^0\)
\(\Rightarrow\widehat{AOC}=\widehat{AOB}=90^0\\ \Rightarrow OC\perp AB\)