Rational Zero Theorem

If $p(x)=a_nx^n+a_{n-1}x^{n-1}+\cdots +a_1x+a_0$ has integer coefficients, then every rational zero of $p$ is of the form $x=\frac{r}{s}$ , where $r$ is a factor of $a_0$ and $s$ is a factor of $a_n$ .