Vì \(\widehat{AOC}\)và \(\widehat{BOC}\)là 2 góc kề bù
\(\Rightarrow\widehat{AOC}+\widehat{BOC}=180^0\)
Gọi \(\widehat{BOC}\)là góc nhọn
\(\Rightarrow0^0< \widehat{BOC}< 90^0\)
Vậy \(90^0< \widehat{AOC}< 180^0\)
\(\Rightarrow\)\(\widehat{AOC}\)là góc tù
Vì \(\widehat{AOC}\) kề bù với \(\widehat{BOC}\)
=> 0o < \(\widehat{AOC}+\widehat{BOC}=180^o\)
Vì \(\widehat{BOC}\) là góc nhọn => 0o < \(\widehat{BOC}\) < 90o
=> 90o < \(\widehat{AOC}\) < 180o
=> \(\widehat{AOC}\) là góc nhọn
Vậy...