Adjoint Differential Equations and Oscillation

The paper offers effective oscillation criteria for the equation [formula] where pi and q are positive continuous functions on an interval [a, ∞) in the case n ≥ 4 is even and the operator [formula] is not in canonical form. The technique is established on properties of adjoint equations of an equation rn(t)(rn−1(t)...(r1(t)(r0(t)y)′)′...)′ + cy = 0 with 0 ≠ c ∈ R and ri(i = 0,1,..., n) positive continuous functions. The conception of adjoint equations is stated in the paper