In this paper, we give a formula, valid for any ring A, which exhibits
the relative K-groups of a truncated polynomial algebra,
Kq(A[x]/(xn),(x)),
in terms of Bokstedt's topological Hochschild homology. In the case
of a perfect field k of positive characteristic, this may be used to
completely calculate the listed K-groups. Indeed, we show that
K2m+1(k[x]/(xn),(x)) = W(m+1)n(k)/VnWm+1(k),
the even dimensional groups being zero. Here Wi(k)
is the ring of big Witt vectors of length i, and Vn :
Wi(k) &rarr Wni(k) is the
nth Verschiebung map. The result extends previous
calculations by Stienstra and Aisbett of
K3(k[x]/(xn),(x)).