\(\left\{{}\begin{matrix}\widehat{A_1}=\widehat{B_1}\\\widehat{B_1}.và.\widehat{A_1}.là.cặp.góc.đối.đỉnh.do.d.cắt.a.và.b\end{matrix}\right.\\ \Rightarrow a//b\\ \left\{{}\begin{matrix}a//b\left(cm.trên\right)\\a\perp c\left(gt\right)\end{matrix}\right.\Rightarrow b\perp c\left(...\right)\)
Nhầm:
\(\left\{{}\begin{matrix}\widehat{A_1}=\widehat{B_1}\\\widehat{B_1}.và.\widehat{A_1}.là.cặp.góc.đồng.vị.do.d.cắt.a.và.b\end{matrix}\right.\\ \Rightarrow a//b\\ \left\{{}\begin{matrix}a//b\left(cm.trên\right)\\a\perp c\left(gt\right)\end{matrix}\right.\Rightarrow b\perp c\left(...\right)\)
