Let $\log$ be the D865: Standard natural real logarithm function.
Let $x_1, \ldots, x_N \in (0, \infty)$ each be a D5407: Positive real number.

Then \begin{equation} \log \left( \prod_{n = 1}^N x_n \right) = \sum_{n = 1}^N \log x_n \end{equation}