Bài 5:
1: AD//BC
nên \(\widehat{A}+\widehat{B}=180^0\)
2: \(\widehat{A}+\widehat{B}=\widehat{C}+\widehat{D}\left(=180^0\right)\)
3: \(\widehat{A}=\dfrac{180^0+20^0}{2}=100^0\)
\(\widehat{B}=180^0-100^0=80^0\)
\(\widehat{D}=\dfrac{2}{3}\cdot180^0=120^0\)
\(\widehat{C}=180^0-120^0=60^0\)



