\(\text{Do }\widehat{A_1}=\widehat{B_3},\text{mà 2 góc này ở vị trí so le trong}\Rightarrow a\text{//}b\left(\text{dấu hiệu nhận biết}\right)\)
\(\Rightarrow\left\{{}\begin{matrix}\widehat{A_4}=\widehat{B_2}\left(\text{so le trong}\right)\\\widehat{A_2}=\widehat{B_4}\left(\text{so le ngoài}\right)\end{matrix}\right.\)
\(\text{Ta có:}\widehat{A_4}+\widehat{A_1}=180^o\left(\text{kề bù}\right)\)
\(\Rightarrow\widehat{A_4}=180^o-120^o=60^o\left(\widehat{A_1}=120^o\right)\)
\(\text{Mà }\text{}\widehat{A_4}=\widehat{B_2}\left(cmt\right)\Rightarrow\widehat{B_2}=60^o\)
\(\text{Lại có:}\widehat{B_4}=\widehat{B_2}\left(\text{đối đỉnh}\right)\Rightarrow\widehat{B_4}=60^o\)
\(\text{Mà }\text{}\widehat{A_2}=\widehat{B_4}\left(cmt\right)\Rightarrow\widehat{A_2}=60^o\)
\(\text{Vậy }\widehat{A_4}=\widehat{B_2}=\widehat{A_2}=\widehat{B_4}=60^o\)