GLOBAL ASYMPTOTIC STABILITY OF ZERO SOLUTION OF NONLINEAR DIFFERENTIAL EQUATIONS OF SECOND ORDER

In contrast with most results obtained by other authors , this paper deals with the differential systems involving four nonlinear items . By use of themethod of constructing the outer bounder of Poincare__ Bendixson region ,a theorem is proved for the global asymptotic stability of zero solution . The conditions in the theorem are much weaker than those given by other authors.