Finding Miller indexes of a vector vertical to known layer

[Sollicitans]

Homework Statement

Find Miller indexes of the vector that is vertical to the layer (211).

Homework Equations

Unknown.

The Attempt at a Solution

I'm not quite sure how to do this. The only thing I came up until now is to invert the numbers (so that I get 1/2, 1 and 1) and then find the vector that is vertical to a vector with these coordinates. But I don't think this is right at all, because this is a layer we are talking about. Not a vector.

 

[drvrm]

I'm not quite sure how to do this. The only thing I came up until now is to invert the numbers (so that I get 1/2, 1 and 1) and then find the vector that is vertical to a vector with these coordinates. But I don't think this is right at all, because this is a layer we are talking about. Not a vector.

your above statement is not clear to me -why not ask a question :
What are Miller indexes in an array of atoms/crystalline arrangements ?