Existence of positive solutions for a neutral differential equation with positive and negative coefficients

This work is concerned with the existence of positive solutions for the neutral delay differential equation with positive and negative coefficients [ x ( t ) − R ( t ) x ( t − r ) ] ′ + P ( t ) x ( t − τ ) − Q ( t ) x ( t − σ ) = 0 , where P , Q , R ∈ C ( [ t 0 , ∞ ) , R + ) , r > 0 , τ ≥ σ ≥ 0 .