show that the line segment joing points p(1,4) and q(5,5) is parrel to the line segment joining points r(3,-4) and s(7,-3)
parallel lines have the same slope (m)
pq ... m = (5 - 4) / (5 - 1) = 1/4
rs ... m = (-3 - -4) / (7 - 3) = 1/4
slopes are the same ... lines are parallel