Let $f, g : \mathbb{R} \to \mathbb{R}$ each be a D5614: Differentiable real function such that

(i)	\begin{equation} h : \mathbb{R} \to \mathbb{R}, \quad h(x) = f(x) g(x) \end{equation}

Then

(1)	$h$ is a D5614: Differentiable real function
(2)	\begin{equation} h'(x) = f'(x) g(x) + f(x) g'(x) \end{equation}