So I'm a bit confused about this question
This question asks for the miller indices for the "families of planes". Is there a single set of Miller indices for each cubic unit cell which I can use to present all of the planes for that unit cell?
For a) I have: $(1, 0, 0)$, $(-1, 0, 0)$
For b) I have: $(0, 1, 0)$, $(0, -1, 0)$, $(0, 3, 0)$, $(0, -3, 0)$
For c) I have: $(3, 2, 0)$, $(-3, -2, 0)$ and I have no idea how to find the others for this one.
Also I noticed that the planes for each cubic unit cell has the same direction. I know that enclosing miller indices in square brackets represents a direction but isn't this just a vector, not a representation of a family of planes?