$\widehat{A4}=32^{\circ};\widehat{A1}=148^{\circ};\widehat{A2}=32^{\circ};\widehat{A3}=148^{\circ}$
a//b suy ra $\widehat{B1}=\widehat{A4}=32^{\circ}$ (cặp góc so le trong)
$\widehat{B1}=32^{\circ}$ suy ra $\widehat{B2}=148^{\circ};\widehat{B3}=32^{\circ};\widehat{B4}=148^{\circ}$