Let T be a time scale with [a, b] {is contained in} T. Later, we consider the existence and multiplicity of positive solutions for the eigenvalue problem y~(Δ~4)(t) - q(t)y~(Δ~2) (σ(t)) = λf(t, y(t)) with the same boundary conditions. We shall also obtain criteria which lead to nonexistence of positive solutions. In both problems, we will use Krasnoselskii fixed point theorem.
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