Ultimate boundedness results for a certain system of third-order non-linear differential equations

We present in this paper ultimate boundedness results for a third-order system of non-linear differential equations of the form $\text{·X + A}\text{X}\text{?}\text{+ B/.X + H(X) = P(t, X, /.X,}\text{X}\text{?}\text{)}$. where A, B are constant symmetric n × n matrices and X, H(X), P(t, X, X, X) are real n-vectors with H:R_n→R_n and P: RXR_nXR_nXR_nXR_n → XR_ncontinuous in their respective arguments. Our results give an n-dimensional analogue of an earlier result of Ezeilo in 1] and extend other earlier results for the case in which we do not necessarily require that H(X) be differentiable.