Vì $\widehat{A_1}$ và $\widehat{A_2}$ là hai góc kề bù
$⇒\widehat{A_1}+\widehat{A_2}=180^o$
mà $\widehat{A_2}=2\widehat{A_1}$
$⇒\widehat{A_1}+2\widehat{A_1}=180^o$
$⇒3\widehat{A_1}=180^o$
$⇒\widehat{A_1}=60^o$
$⇒\widehat{A_2}=2.60^o=120^o$
Vì $c⊥a,c⊥b$
$⇒a//b$
$⇒\widehat{A_1}=\widehat{B_1}=60^o$ (so le ngoài)
$⇒\widehat{A_2}=\widehat{B_2}=120^o$ (so le trong)
Vậy $\widehat{A_1}=\widehat{B_1}=60^o$
$\widehat{A_2}=\widehat{B_1}=120^o$
