Answer
$$ - \frac{1}{a(a+h)}$$
Work Step by Step
For part a, replace wherever you see an x with a+h. This gives:
$$ \frac{1}{a+h}$$
For part b, replace wherever you see an x with a. This gives:
$$ \frac{1}{a}$$
Now, we are asked to plug the answers from a and b into the equation:
$$ \frac {f(a+h)-f(a)}{h}$$
We substitute to find:
$$\frac{\frac{1}{a+h} - \frac{1}{a}}{h}$$
Lastly, we simplify using the techniques learned in this chapter. This gives:
$$ - \frac{1}{a(a+h)}$$
