Last minute question!
If you have a line, say (1,2,3) + lambda(2,0,1) and you want to find the coordinates of a point on the line, which you know to be perpendicular (from the line to the origin) how would you work out it's coordinates?
I thought you would dot product (x,y,z) and (2,0,1) and then get: 2x+z=0. Then I would sub in random numbers, like x=2, to find z=-4, to get (2,0,-1), but this isn't correct apparently. :-S