ANSWER:
STEP-BY-STEP EXPLANATION:
We have that angle 1 and angle 2 are supplementary, thanks to the theorem that states that 2 adjacent angles whose exterior rays form a line are supplementary.
From the above we can determine that angles 2 and 3 are equal. (consecutive interior angles). Due to the above, angles 1 and 3 are equal, by transitive property.
We also have to angle 1 = angle 3 (corresponding angles).
If 2 lines are cut by a transversal so that corresponding angles are congruent (angle 1 and angle 3), then the lines are parallel (corresponding converse theorem).
