How to calculate the surface atom density of an fcc(111) surface?

[osc_wildly]

How do you calculate the surface atom density of an fcc(111) surface expressed in terms of a?

I've managed to do it for fcc(100) and fcc(110), but I can't seem to figure it out for fcc(111).

Any help would be greatly appreciated!

 

[osc_wildly]

nevermind

Not very helpful...

 

[vincent_vega]

well all of the lengths are going to be diagonals right? (since the plane is a triangle) just use the quadratic formula to the the lengths. Then since all the lengths are the same all the angles are 60 deg. so use geometry to find the height of the triangle. With that you can find the area. Then just find how much of the atoms are enclosed by the plane.