Jacob's ladders, interactions between $ζ$-oscillating systems and $ζ$-analogue of an elementary trigonometric identity
In our previous papers, we have introduced within the theory of the Riemann zeta function the following notions: Jacob's ladders, oscillating systems, $ζ$-factorization, metamorphoses, \dots In this paper we obtain $ζ$-analogue of an elementary trigonometric identity and other interactions between oscillating systems.