Answer:
The slope of AB is undefined; the slope of CD is 0; The lines are perpendicular.
Step-by-step explanation:
Line AB would form a vertical line. Slope is Δy/Δx. To go from 3 to 7 (the y-coordinates) you need to go up 4 units. So we would then have Δy/Δx = 4/Δx. To go from -5 to -5 (the x-coordinates) we have to go left or right 0 units. So, Δy/Δx = 4/Δx = 4/0. Anything divided by 0 is undefined. Remember: vertical lines always have an undefined slope.
Line CD would form a horizontal line. To go from 9 to 9 (the y-coordinates) you need to go up or down 0 units. So, Δy/Δx = 0/Δx. To go from 1 to -10 (the x-coordinates) you need to go down 11 units. So Δy/Δx = 0/Δx = 0/1. 0 divided by anything is 0. Remember: horizontal lines always have a slope of 0.
If you picture a horizontal line and a vertical line intersecting, they would both form a right angle when they intersect. By definition, this would make both lines perpendicular.
