研究一类三次微分系统{dx/dt=-y(ax^2+bx+1)+Dx-lx^3 dy/dt=x(ax^2+bx+1)在a=0,b≠0与b2=4a两种情形下,讨论该系统极限环的存在性和唯一性.
A class of cubic differential systems is investigated:{dx/dt=-y(ax^2+bx+1)+Dx-lx^3 dy/dt=x(ax^2+bx+1)For this system with a=0,b≠0 and b^2=4a,the conditions for the existence and uniqueness of limit cycles are investigated.