Ta có: AD//BC(gt)
\(\Rightarrow\widehat{A_2}=\widehat{C}=30^0\)(so le trong)
Ta có: AD//BC(gt)
\(\Rightarrow\widehat{BAD}+\widehat{B}=180^0\)(trong cùng phía)
\(\Rightarrow\widehat{A_1}+\widehat{A_2}+\widehat{B}=180^0\)
\(\Rightarrow\widehat{A_1}=180^0-\widehat{A_2}-\widehat{B}=180^0-30^0-70^0=80^0\)