“…As we know, system (1) in various types have been extensively studied and gained wide attention in decades [9,13,8,13,14,15,21,16,17,11,15,5,24,25,27,28,19]. One of the particularities of this system is that each limit cycle surrounding the origin can be expressed in generalized polar coordinates as r = r(θ), with r(θ) being a smooth periodic function, see for instance [8,13,14,15,19], etc.…”