Forced Oscillation of nth-Order Functional Differential Equations

In this paper we investigate the oscillation of forced functional differential equations xŽn.Žt. aŽt.fŽxŽqŽt... eŽt., when the forcing term eŽt. is not required to be the nth derivative of an oscillatory function. Some new oscillatory criteria are given. We also apply our technique to the forced neutral differential equation of the form ŽxŽt. cxŽt ..Žn. aŽt.xŽt. bŽt.xŽt . eŽt. cŽt.f1ŽxŽt.. dŽt.f2ŽxŽt .., where xf1Žx. 0 and xf2Žx. 0 for x 0; n 1; , are nonnegative constants; aŽt. 0; bŽt. 0; cŽt. 0; dŽt. 0; which includes the special case f1Žx. x sgn x, f2Žx. x sgn x, 1 and 1.