Perpendicular or Parallel?

Question

One line passes through the points (−7,−4) and (5,4). Another line passes through points (−4,6) and (6,−9). Are the lines perpendicular or parallel?

Answer 1

Just fine their slopes.

m = (y₂ - y₁)/(x₂ - x₁)

m = (4 + 4)/(5 + 7) = 8/12 = 2/3

m = (-9 - 6)/6 + 4) = -15/10 = -3/2

Since the slopes are negative reciprocals, the lines are perpendicular.