Abstract
The objective of this paper is to present an analytical investigation to analyze the
                   vibration of parametrically excited oscillator with strong cubic negative nonlinearity based on
                    Mathieu-Duffing equation. The analytic investigation was conducted by using He's 
                    homotopy-perturbation method (HPM). In order to obtain the analytical solution of Mathieu-Duffing 
                    equation, homotopy-perturbation method has been utilized. The Runge-Kutta's (RK) algorithm 
                    was used to solve the governing equation via numerical solution. Finally, to demonstrate the validity 
                    of the proposed method, the response of the oscillator, which was obtained from approximate
                     solution, has been shown graphically and compared with that of numerical solution. Afterward, the
                      effects of variation of the parameters on the accuracy of the homotopy-perturbation method were 
                      studied.