Tunç, C.2025-05-102025-05-1020110717-627910.4067/S0716-091720110001000042-s2.0-79959383064https://doi.org/10.4067/S0716-09172011000100004https://hdl.handle.net/20.500.14720/6657In this paper, we give some sufficient conditions on the instability of the zero solution of a kind of eighth order nonlinear differential equations of retarded type by using the Lyapunov direct method. The obtained sufficient conditions improve an existing result in the literature.eninfo:eu-repo/semantics/openAccessDelay Differential EquationEighth OrderInstabilityThe Lyapunov Direct MethodArticle