Hình vẽ thì bạn tự vẽ nha
Giải:
Trong \(\Delta OBC:\widehat{BOC}+\widehat{OBC}+\widehat{OCB}=180^o\left(gt\right)\)
\(\Rightarrow\widehat{OBC}+\widehat{OCB}=180^o-\widehat{BOC}=50^o\)
Mà \(\widehat{OBC}+\widehat{OCB}=\frac{\widehat{ABC}}{2}+\frac{\widehat{ACB}}{2}=\frac{\left(\widehat{ABC}+\widehat{ACB}\right)}{2}\)
Nên \(\frac{\widehat{ABC}}{2}+\frac{\widehat{ACB}}{2}=50^o\)
\(\Rightarrow\widehat{ABC}+\widehat{ACB}=100^o\)
Trong \(\Delta ABC:\widehat{BAC}+\widehat{ABC}+\widehat{ACB}=180^o\left(gt\right)\)
\(\Rightarrow\widehat{BAC}=180^o-\left(\widehat{ABC}+\widehat{ACB}\right)\)
\(\Rightarrow\widehat{BAC}=180^o-100^o\)
\(\Rightarrow\widehat{BAC}=80^o\)
