Áp dụng tc dstbn:
\(\widehat{A}=2\widehat{B}=2\widehat{C}=4\widehat{D}\Rightarrow\dfrac{\widehat{A}}{4}=\dfrac{\widehat{B}}{2}=\dfrac{\widehat{C}}{2}=\dfrac{\widehat{D}}{1}=\dfrac{\widehat{A}+\widehat{B}+\widehat{C}+\widehat{D}}{4+2+2+1}=\dfrac{360^0}{9}=40^0\\ \Rightarrow\widehat{A}=40^0\cdot4=160^0\)