Chapter 11 - Section 11.5 - Derivatives of Logarithmic and Exponential Functions - Exercises - Page 842: 34

$ -\displaystyle \frac{2}{x-8}$

Apply the power rule for logarithms $s(x)=-2\ln(x-8)$ Apply $\displaystyle \frac{d}{dx}[\ln|u|]=\frac{1}{u}\cdot\frac{du}{dx}$, with constant multiple, $s^{\prime}(x)=-2\displaystyle \cdot\frac{1}{x-8}\cdot 1=$ $=-\displaystyle \frac{2}{x-8}$