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On the oscillation of solutions of a class of linear fourth order differential equations. (English) Zbl 0547.34023
Consider the equation (*) $$y^{(4)}+P(t)y''+R(t)y'+Q(t)y=0$$, where P(t), R(t), and Q(t) are real-valued continuous functions on [a,$$\infty)$$. The author shows the existence of monotonous solutions of (*) under the assumptions that P(t)$$\leq 0$$, $$R^ 2(t)\leq 2P(t)Q(t)$$ for all $$t\in [a,\infty)$$, and Q(t) is not identically zero in any subinterval of [a,$$\infty)$$. The author gives conditions for conjugation of equation (*) and necessary and sufficient conditions for (*) to be oscillatory and nonoscillatory respectively. The condition for oscillation is in terms of the behaviour of nonoscillatory solutions.
Reviewer: T.S.Liu

MSC:
 34C10 Oscillation theory, zeros, disconjugacy and comparison theory for ordinary differential equations 34A30 Linear ordinary differential equations and systems
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References:
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