Trong \(\Delta ABC\) có : \(\widehat{A}+\widehat{B}+\widehat{C}=180^0\)
\(\Rightarrow\widehat{A}+\widehat{C}=180^0-\widehat{B}=180^0-80^0=100^0\)
Ta có : \(3A=2C\Rightarrow\dfrac{\widehat{A}}{2}=\dfrac{\widehat{C}}{3}\)
Áp dụng tính chất dãy tỉ số bằng nhau, ta có :
\(\dfrac{\widehat{A}}{2}=\dfrac{\widehat{C}}{3}=\dfrac{\widehat{A}+\widehat{C}}{2+3}=\dfrac{100^0}{5}=20^0\)
\(\Rightarrow\widehat{A}=20^0.2=40^0\)
\(\Rightarrow\widehat{C}=20^0.3=60^0\)