How would you show that the derivative of $\displaystyle f(x) = \frac{1}{\sqrt{x}}$ is equal to $\displaystyle \frac{1}{2\sqrt{x^3}}$ for $\displaystyle x>0$ , using the definition of a derivative??

I started and got lost in the calculation...

I have to start with the following

$\displaystyle | \frac{\frac{1}{\sqrt{x}}-\frac{1}{\sqrt{c}}}{x-c} + \frac{1}{2\sqrt{c^3}} |$ and show I can make it less than $\displaystyle \epsilon$ , which is just the definition

I know I have $\displaystyle |x-c|<\delta$ to play with... can anyone help me out? this is due tomorrow so the more you can give me the better lol thanks