“…Our approach is variational and due to the form of the corresponding functional, it is based on a detailed study of the Nehari's manifold together with Ekeland's Variational Principle [15], a Riesz's representation theorem for some Sobolev spaces [12], the Mountain Pass Theorem [2], the Fountain and Dual Fountain Theorems [4,6,23], some arguments based in the Krasnoselskii genus theory found in [17] and compactness arguments, either derived from the subcriticality nature of the problem, or from the Concentration-Compactness Principle [20] employed in the case when the equation has a critical exponential growth.…”