Question

find the intersection of the following lines.

r1 = [2,1,1] + t[4,0, -1] and r2 = [3, -1, 1] + s[9, -2, -2]

Answer 1

just set them equal:
1 = -1-2s
s = -1
2+4t = 3+9s = 3-9
t = -2
so, trick question -- the lines do not intersect