Abstract: In this paper, we study rhe problems of bifurcation in nonlinear oscillation system under combined parametric and forcing excitation for 1/2 su-bharmonic resonance-primary parametric resonance. The eight different diagrams of bifurcating response curve are obtained by using the method of multiple scales.In this paper, we study rhe problems of bifurcation in nonlinear oscillation system under combined parametric and forcing excitation for 1/2 su-bharmonic resonance-primary parametric resonance. The eight dif...