Existence for Nonoscillatory Solutions of Higher-Order Nonlinear Differential Equations

The existence of nonoscillatory solutions of the higher-order nonlinear differential equation [r(t)(x(t)+P(t)x(t-τ))(n-1)]′+∑i=1mQi(t)fi(x(t-σi))=0, t≥t0, where m≥1,n≥2 are integers, τ>0, σi≥0, r,P,Qi∈C([t0,∞),R), fi∈C(R,R) (i=1,2,…,m), is studied. Some new sufficient conditions for the existence of a nonoscillatory solution of above equation are obtained for general Qi(t) (i=1,2,…,m) which means that we allow oscillatory Qi(t) (i=1,2,…,m). In particular, our results improve essentially and extend some known results in the recent references.