New oscillation criteria for a class of second-order nonlinear forced differential equations

By using classical variational principle and averaging technique, new oscillation criteria are established for second-order nonlinear forced differential equations [r(t) psi (x (t)) phi (x'(t))]'+ q (t) f (x (t)) = e (t), t >= t(0), where the functions r, q, e is an element of C ([t(0), infinity), R), and phi, psi, f is an element of C(R, R) improve and extend some recent results. (c) 2007 Elsevier Inc. All rights reserved.