If $f(x) = \frac{1}{x^{8}}+\frac{1}{x^{6}}$ then $\frac{df}{dx} =$
The slope of the tangent line to $f$ at $x = -6$ is
If $T(x) = \frac{1}{x^{8}}+\frac{1}{x^{6}}$ is the temperature of a runner (in Fahrenheit) at a distance x from the start line (in miles) find the rate at which the runners temperature is changing with respect distance at $x = 9$ with units: