  We study the curved Koszul duality theory for associative algebras presented
by quadratic-linear-constant (QLC) relations. As an application, we investigate
the cyclic (co)homology of a QLC algebra and its Koszul dual curved DG algebra,
and extend a result due to Feigin and Tsygan. We also study a commutative/Lie
analog of this curved Koszul duality theory.
