Content of Rational Polynomial is Multiplicative

Theorem
Let $h \in \Q \left[{X}\right]$ be a polynomial with rational coefficients.

Let $c_h = \operatorname{cont} \left({h}\right)$ denote the content of $h$.

Then for any polynomials $f, g \in \Q \left[{X}\right]$ with rational coefficients:
 * $\operatorname{cont} \left({f g}\right) = \operatorname{cont} \left({f}\right) \operatorname{cont} \left({g}\right)$

Proof
Let $\tilde f = c_f^{-1} f$, $\tilde g = c_g^{-1} g$

By Content of Scalar Multiple:
 * $c_{\tilde f} = c_{\tilde g} = 1$

That is, $\tilde f$ and $\tilde g$ are primitive.

By Gauss' lemma, it follows that $\tilde f \tilde g$ is primitive.

Now,