Given that;
[tex]\angle1\cong\angle3,\angle12\cong\angle8[/tex]
Line a and b are two straight lines cut by two transversal lines l and m.
The tranversal line l shows that;
[tex]\begin{gathered} \angle8\cong\angle6 \\ \end{gathered}[/tex]
But also;
[tex]\angle8\cong\angle12[/tex]
Thus,
[tex]\angle6\cong\angle12[/tex]
Then, if two lines are cut by a transversal so the corresponding angles are congruent, then the lines are parallel.
Thus, line l is parallel to m
