Given a polynomial $f \in \mathbb{C}[x_1,\ldots,x_n]$, then how can I prove that $f(a_1,\ldots,a_n) = 0$ implies $f$ is a summation of factors of $x_i - a_i$ for $i \in \{1,\ldots, n\}?$
This is not at all obvious to me. Any help would be much appreciated!