The solution of the problem 3.39 кр 3 from the problem

The solution of the problem 3.39 кр 3 from the problem

Task 3.39
A narrow beam of X-rays with a wavelength of 0.095 nm falls on the face of the rock salt crystal. What should be the angle of slip of the rays in order to observe the third-order diffraction maximum? The distance between the atomic planes of the crystal is 0.285 nm.