Use the definition of the derivative to find f' (x).

f (x)= $\displaystyle \frac {1}{x^2}$

f'(x)= $\displaystyle {\lim_{\Delta x \rightarrow 0}} \frac{\frac {1}{(x+ \Delta x)^2} - \frac {1}{x^2}} {\Delta x}$

Should I get a common denominator in the top of the problem?