1. The problem statement, all variables and given/known data The unit cell in a cubic crystal is 2.74Å. Determine the Bragg angle for reflections from the planes (200), (212) and (-112). [sorry i dunno how to put a bar on top of the numbers] if the x-ray wavelength used is 1.54Å 2. Relevant equations Given Bragg's condition as 2d sinθ = nλ and d = 2π /|G| where G = ha* + kb* + lc* according to Laue condition. there's also d = a /√(h^2 + k^2 + l^2 ) where a is the edge length. 3. The attempt at a solution Since d is the distance between planes in atomic lattice, I guess it meant the distance of (200), (212) and (-112) to the origin. So I calculated is by finding the magnitude of G. Then i got confused by the two d equations. Should I use 2π or a to divide with |G| to find the Bragg angle? I thought a is more logical, but the 2π /|G|[/I] is making me confused. What are the difference between them?