OSCILLATORY PROPERTIES OF SECOND ORDER NONLINEAR DIFFERENTIAL EQUATIONS

Necessary and sufficient conditions for oscillation and non-oscillation of the differential equation u '' + f(t, u, u') = 0 are given, where f : [a, + infinity) x R-2 -> R is a continuous function such that f(t, x, y)x >= 0 for t >= a, x and y is an element of R. The results obtained extend recent results of [21-23] stated for the equation u '' + h(t)g(u) = 0, where g(x)x > 0 for x not equal 0. Some examples illustrating the sharpness of oscillation criteria are also given.