What Is the Angle Between the (111) and (1̅10) Planes in a Cubic Lattice?

[Frinkz]

Homework Statement

Indicate the (111) and ([11]0) ([11] has an over line, so is negative, don't know how to do on forums!) planes in a cubic lattice in a diagram, then calculate the angle between them.

The Attempt at a Solution

I think I have drawn this right (see attatchment), but I am not sure what angle it is referring to.

I would guess it is 90 degrees (in red), but I doubt I would be asked this, maybe the other angle (purple), could someone give any thoughts?

Also if my drawing is wrong, let me know! I wasn't 100% sure about the negative (110)

 

[nasu]

Take the angle between the normals to the planes. It will eliminate ambiguity and it will be much easier. You should know what vector is normal to the plan (h k l) if you studied reciprocal lattice.