For which set of lines is it reasonable to state that the two lines are almost perpendicular to each other?
a. y = 2.1x 3, y = 2.1x 5
b. y = 0.9x 5, y = -1.26x 8
c. y = 5x 1.25, y = -5x 1.25
d. y = 3/4x 0.28, y = 4/3x 0.29