Hello, I'm trying to do a review of functions and I'm having difficulty on this one:

$\displaystyle f(x) = \frac 1x$

The problem is

$\displaystyle \frac {f(x) - f(a)}{x-a}$

I've tried a few possible ways, getting the denominators the same in the numerator. No luck. Probably missing something simple.

Can someone point me in the right direction?