Question

two lines pass through the origin. The lines have slopes that are opposites. Compare and contrast the lines.

Answer 1

If the lines have different signs for their slopes, that means that in one equation, as x increases, y decreases. And in the second equation, as  increases, y decreases. They will both have the same y intercept however, because they both pass through the origin. 
Hope this helps.

Answer 2

Well, since one has a negative rate of change, and one positive, they would form an X through the graph. That could or could not mean they have equal slopes. We also know that their y intercepts would be 0, since they pass through that.