Two parallel lines are crossed by another line and formed angles
The pair of angles inside the traversal line is consecutive interior angles
We look at the pair of angles inside the parallel lines
Inside the parallel lines we have angle 2, 3 , 1 and 4
Angle 3 and angle 4 are consecutive interior angles
Also angle 2 and angle 1 are consecutive interior angles
angle 4 is a consecutive interior angle with angle 3