Oscillation theorems for linear differential equations of second order (Q1112993)

Some new oscillation criteria are given for second order ordinary differential equations of the form \(x''(t)+a(t)x(t)=0,\) \(t\geq t_ 0\), where a is a continuous real-valued function on the interval \([t_ 0,\infty)\) without any restriction on its sign. These criteria extend and improve previous oscillations results due to \textit{I. V. Kamenev} [Mat. Zametki 23, 249-251 (1978; Zbl 0386.34032)] and \textit{J. Yan} [Proc. Am. Math. Soc. 98, 276-282 (1986; Zbl 0622.34027)]. The results obtained can be applied in some cases in which other known oscillation theorems are not applicable.