Positive solutions of second-order boundary value problems with sign-changing nonlinear terms ✩

In this paper the existence results of positive solutions are obtained for second-order boundary value problem −u = f (t,u), t ∈ (0, 1), u(0) = u(1) = 0, where f ∈ C([0, 1] × R+), whose sign may change. The proof is based on the fixed point index theory in cones.  2003 Elsevier Science (USA). All rights reserved.