研究三次系统{dx/dt=-y(ax^+bx+1)+Dx-lx^3 dy/dt=x(ax^2+bx+1) 在a=0,b≠0,D≥l/b^2与b^2=4a,b≠0,D≥4l/b^2 时,该系统极限环的存在性问题,证明了系统在上述条件下均不存在极限环.
A class of cubic differential systems is investigated: {dx/dt=-y(ax^+bx+1)+Dx-lx^3 dy/dt=x(ax^2+bx+1) For this system, we investigated the existence of limit cycles under conditions:a=0,b≠0,D≥l/b^2 and b^2=4a,b≠0,D≥4l/b^2.We proved that there is no any limit cycles under above conditions.