EXISTENCE AND MULTIPLICITY OF PERIODIC SOLUTIONS TO AN INDEFINITE SINGULAR EQUATION WITH TWO SINGULARITIES. THE DEGENERATE CASE

摘要

We analyze the existence of T-periodic solutions to the second-order indefinite singular equatiou '' = beta h(t)/cos(2)uwhich depends on a positive parameter beta 0. Here, h is a sign-changing function with (h) over bar = 0 and where the nonlinear term of the equation has two singularities. For the first time, the degenerate case is studied, displaying an unexpected feature which contrasts with the results known in the literature for indefinite singular equations.