Hi
Using the point-slope formula,
P1(4,-5)
P2(6,-9) m = 4/-2 = -2
Q1(5,-4)
Q2(1, 4) m = -8/4 = -2
line through P1 and P2 is parallel to the line through Q1 and Q2.
P1(5, 1)
P2(3,-2) m = 3/2
Q1(0,-2)
Q2(3,-4) m = 2/-3 = -2/3
line through P1 and P2 is perpendicular to the line through Q1 and Q2.
P1(1,-1)
P2(3,-2) m = 1/-2 = -1/2
Q1(-4,1)
Q2(2,-5) m = 6/-6 = -1
the line through P1 and P2 is neither parallel nor perpendicular
to the line through Q1 and Q2.