The reason why linear pairs and vertical angles are used to prove lines are parallel is because they area transversal drawn through the parallel lines will form angles on each of the two parallel lines including;
1) Supplementary linear pairs and
2) Vertical angles
3) Alternate angles
Given that either;
a) The corresponding angles that form the linear pairs are congruent
b) The corresponding vertically opposite angles are congruent
c) The corresponding alternate angles are congruent, we have;
