Triple positive radial solutions arising from biharmonic elliptic systems

We study, according to topological approaches, the solvability of systems for biharmonic equations with Navier boundary conditions. New sublinear conditions for the existence of positive solutions are established. In addition, the most interesting part of this article is that the Leggett–Williams fixed point theorem is first used to analyze the existence of triple positive radial solutions for biharmonic elliptic systems. The uniqueness and multiplicity of positive radial solutions are also discussed. Two examples are presented to illustrate the applicability of our main results.