How to find the Miller indices for a family of planes?

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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?

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asked Nov 30, 2017 at 14:13

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