1) This is the given premise "line p is parallel to line q"
2) Angles 1 and 2 are equal (congruent) because they are vertical opposite angles.
3) Angles 2 and 3 are equal (congruent) because they are alternate angles.
4) Angles 3 and 4 are equal (congruent) because they are vertical opposite angles.
5) Angles 1 and 4 are equal (congruent) because: a) angle 1 is equal to angle 2 being vertical opposite, b) angle 2 is equal to angle 4 because they are corresponding angles, therefore c) due to transitive property, angle 1 will equal angle 4.
