Using variational arguments we study the non-existence and multiplicity of non-negative solutions
for a class equations of the form -div(a(x,?? u)) =? f(x,u) in ??, where ?? is a bounded domain in RN, N ??3,
f is a sign-changing Carath??odory function on???? [0, +??) and ?is a positive parameter. ?? 2009 Glasgow
Mathematical Journal Trust.