A wave chain formed by the two monochromatic de Broglie waves
The paper presents the research of a quantum system in three-dimensional space. The system is formed by two elements, which have the same mass and are moving with fixed nonrelativistic unidirectional velocity. In this case, it means that the wave functions of the elements are de Broglie plane monochromatic waves. Were proved the two theorems both of which relate the group velocity of a wave packet formed by elements with harmonic parameters. The first theorem states that the group velocity is equal to the ratio of difference between the cyclic frequencies of the harmonics and the difference of their wave numbers. In this regard was noted that the formula in which the group velocity is equal to the derivative of the cyclic frequency of a wave number is the limiting case of the proved theorem. The second theorem states that the group velocity of the wave packet is equal to the sum of the phase velocities of its harmonics.