Question

giải chi tiết ạ

Answer 1

Đặt \(\widehat{CAB}=a;\widehat{ABC}=b;\widehat{ACB}=c\)

Theo đề, ta có: a-b=b-c=20

=>a=b+20; c=b-20

Xét ΔABC có \(\widehat{ABC}+\widehat{ACB}+\widehat{BAC}=180^0\)

=>\(b+b+20+b-20=180\)

=>3b=180

=>b=60

=>\(\widehat{ABC}=60^0\)

\(\Leftrightarrow\widehat{ACB}=60^0-20^0=40^0\)

=>\(\widehat{AOB}=2\cdot40^0=80^0\)

=>Chọn D