The paper deals with the forced second-order linear differential equation
where , are continuous functions. The author presents two oscillation criteria for equation (1) that do not assume that and be of definite sign.
In theorem 1, a result of M.A. El-Sayed [Proc. Am. Math. Soc. 118, 813-817 (1993; Zbl 0777.34023)] is extended. The second criterion is derived under the assumption that the unforced equation is nonoscillatory.
Two examples are given to show how the results can be applied where previous results are inconclusive.