[G O D I V A]

For a BCC why does a = 4r/√3
for FCC why does a = 4r/√2
and for HCP why does a = 2r

I've seen the pictures, but I just dont understand how they get those values

For example on this powerpoint: http://faculty.ksu.edu.sa/3371/p324/324-1-Crystallography%20and%20Crystal%20Structures%5B.pdf

slide 26 for BCC
and slide 31 for FCC

[Borek]

pdf is not powerpoint.

These can be calculated from simple geometry and Pythagorean theorem, you just have to select correct surface on which to calculate distance between centers of the spheres (atoms).

[G O D I V A]

ok thanks