The line l and m are parallel and intersected by transversal line t.
The angle 4 and angle 8 is pair of correspoding angles. So,
[tex]\angle4=\angle8[/tex]
The angle 1 and angle 8 are pair of alternte exterior angles. So,
[tex]\angle1=\angle8[/tex]
Thus angle 1 and angle 4 are congurent to angle 8.
