“HOMOTOPY PERTURBATION METHOD (HPM), ADOMIAN DECOMPOSITION METHOD (ADM) AND COUPLING HPM AND PEM (PARAMETER-EXPANSION METHOD) FOR NONLINEAR OSCILLATOR WITH COORDINATE-DEPENDENT MASS”. 2025. Far East Journal of Mathematical Sciences (FJMS) 142 (4): 615-37. https://doi.org/10.17654/0972087125034.