Periodic solutions for a kind of Liénard equation with a deviating argument

In this paper, the Liénard equation with a deviating argument x ″ ( t ) + f 1 ( t , x ( t ) ) x ′ ( t ) + f 2 ( x ( t ) ) ( x ′ ( t ) ) 2 + g ( t , x ( t − τ ( t ) ) ) = p ( t ) is studied. By applying the coincidence degree theory, we obtain some new results on the existence and uniqueness of T -periodic solutions to this equation. Our results improve and extend some existing ones in the literature.