NONLINEAR OSCILLATIONS, cilt.12, sa.1, ss.123-132, 2009 (SCI-Expanded)
The main purpose of this paper is to give a result with explanatory example that deals directly with the instability of the trivial solution of a certain nonlinear vector differential equation of the fourth order. The result established here improves and includes a well-known instability result established for a scalar nonlinear differential equation of the fourth order.