“…The most commons and most widely studied methods of all approximation methods for nonlinear differential equations are perturbation methods [1]. Some of other techniques include variational and variational iteration methods [4][5][6][7][8][9][10][11][12], exp-function [13,14], homotopy perturbation [15][16][17][18][19][20][21][22], equivalent linearization [23,24], standard and modified Lindstedt-Poincaré [25][26][27][28][29], artificial parameter [30,31], parameter expanding [32][33][34], harmonic balance methods [1,[35][36][37][38][39][40], etc. Surveys of the literature with numerous references and useful bibliography and a review of these methods can be found in detail in [28] and [41].…”