Oscillation criteria for a class of nonlinear system of differential equations

Using the integral average method, we establish some oscillation criteria of Kamenev type and Yan type for the nonlinear system of differential equation u i ʹ = | u 3 − i | λ i sgn ⁡ u 3 − i + ( − 1 ) i − 1 b i ( t ) u i , ( i = 1 , 2 ) where the functions bi(t) (i = 1, 2) are nonnegative and summable on each finite segment of the interval Z0, ∞), λi > 0 (i = 1,2) with λ1 λ2 = 1.