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

(i)	\begin{equation} h : = f g \end{equation}

Then

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