“…The Max-min [6], the parameter-expanding approach [7], frequency-amplitude formulation [8], the Variational Iteration [9], perturbation techniques [10,11,12], the iteration perturbation [13], the Homotopy Analysis [14,15], the Energy Balance analysis [16], the harmonic balance [17], the equivalent linearization method (ELM) [18,19] and 20 the Extended Lindstedt-Poincare approach [20] are some examples of these techniques. Each of these methods has some strong points and some weakness.…”