The greatest common factor is the biggest factor that divides two different numbers. For example, the greatest common factor of 6 and 8 is 2. The least common multiple is the smallest number that two numbers share as a multiple. For example, 12 is a the lowest common multiple of 3 and 4.
Okay well, if you make a graph, Point A (7,0) and Point B (4,6) are in the top right quadrant. and Point C (1,1) and Point D (5,3) are in the top left, top right, and bottom left quadrant (I'll link a photo of the graph.) so the lines intersect and make it perpendicular