Let $R$ be a ring and $f(X) \in R[x]$ be a non-constant polynomial. We know that the number of roots, of $f(X)$ in $R$ has no relation, to its degree if $R$ is not commutative, or commutative but not a domain. But,
- The number of roots, of a non-zero polynomial over commutative integral domain, is at most its degree.
How does one prove above result?