a: Khi a=50 độ thì \(\widehat{B}=\widehat{C}=65^0\)
Khi a=60 độ thì \(\widehat{B}=\widehat{C}=60^0\)
Khi a=70 độ thì \(\widehat{B}=\widehat{C}=55^0\)
b:
1: \(\widehat{ABC}+\widehat{ACB}=110^0\)
=>\(\widehat{OBC}+\widehat{OCB}=55^0\)
hay \(\widehat{BOC}=125^0\)