This is for body-centered cubic crystal structure. 1. The problem statement, all variables and given/known data Prove a = 4R/sqrt(3). R is the radius of sphere and a is the edge of the cell (cubic). The image attached will be cut into cube so that 4 outter spheres' centers will be the edges of the cube, a. 2. Relevant equations n/a 3. The attempt at a solution Well, the disagnal from the farthest two points are 4R. I tried to use one face to calculate the diagnal edge of the face and form a triangle with 4R and sqrt(2) but it won't work. Something is wrong...please help!