I'm stuck on this question: Let S be a level surface defined by f (x, y, z) = k where k is a constant. Show that the two possible orientations of S can be chosen as ± ∇f / ‖∇f ‖
I believe in order to prove this I need to use the dot product, but I am not sure which vectors to include in the dot product calculation. Any help and suggestions would be appreciated. Thank you.