Question

Powder specimens of three different monoatomic cubic crystals are analyzed with a Debye-Scherrer camera. It is known that one sample is fcc, one is bcc, and one has the diamond structure. The approximate positions of the first four diffraction rings in each case are: A: 42.2, 49.2, 72.2, 87.3; B: 28.8, 41.0, 50.8, 59.6; C: 42.8, 73.2, 89.0, 115.0 (a) Identify the crystal structures of A, B, and C. (b) If the wavelength of the incident x-ray beam is 1.5Å, what is the length of the side of the conventional cubic cell in each case?

There is already an answer on Chegg for this question, but it doesnt elaborate on why things were done, I don't understand how to work backwards from the angles to get the structure

Answer 1