B: (4, 3, 7)
A: (1, -2, 3)
u = Vector(A, B)
f = OrthogonalLine(B, xOyPlane)
g = OrthogonalLine(A, xOyPlane)
B' = Intersect(f, xOyPlane)
A' = Intersect(g, xOyPlane)
v = Vector(A', B')