Let $\log_a$ be the D866: Standard real logarithm function in base $a \in (0, \infty) \setminus \{ 1 \}$.
Let $x, y \in (0, \infty)$ each be a D5407: Positive real number.

Then \begin{equation} \log_a \frac{x}{y} = - \log_a \frac{y}{x} \end{equation}