Let
$R$ be a unit-regular ring and let
$\sigma $ be an endomorphism of
$R$ such that
$\sigma \left( e \right)\,=\,e$ for all
${{e}^{2}}\,=\,e\,\in \,R$ and let
$n\,\ge \,0$. It is proved that every element of
$R[x;\,\sigma ]/\left( {{x}^{n+1}} \right)$ is equivalent to an element of the form
${{e}_{0}}\,+\,{{e}_{1}}x\,+\,\cdots \,+\,{{e}_{n}}{{x}^{n}}$, where the
${{e}_{i}}$ are orthogonal idempotents of
$R$. As an application, it is proved that
$R[x;\,\sigma ]/\left( {{x}^{n+1}} \right)$ is left morphic for each
$n\,\ge \,0$.