Question

Which lines are parallel if m4 = m5? Justify your answer.

Answer 1

Ok to start with the answer,
 Opposite angles formed by two intersecting lines are equal, so angle 1 is the same as angle 4.
That means angle 1 = angle 5 as well. 

When a line intersects two parallel lines, the corresponding angles are equal. That is, if r and s are parallel, then the angles formed when l intersects r are the same s the angles formed when l intersects s.
Angle
 1 = Angle 5,
Angle 2 = Angle 6, and so forth.
Since we know
angle 1 = angle 5,
we can conclude that r and s are parallel.