Definition: A polynomial $f\in \mathbb{Z}[x]$ with $f(x)=a_0+a_1x+\dots+a_nx^n$ is a primitive polynomial the only common factors of $a_0,a_1,\dots,a_n$ are the units $\pm 1\in \mathbb{Z}$ and if $a_n>0$.
I stumbled across this sentence in my course notes, but I can't find a reasonable explanation for it:
Every polynomial $f\in\mathbb{Q}[x]$ can be uniquely written as a product $f(x)=c\cdot f_0(x)$ with $c\in\mathbb{Q}$ and $f$ a primitive polynomial in $\mathbb{Z}[x]$.
Thanks.