Find the derivative using the definition only!

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

I started and got lost in the calculation...

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

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

If you're looking to find the derivative from the definition, check out this thread: http://www.mathhelpforum.com/math-he...ve-answer.html

But it looks like you're trying to prove the existence of a limit.

thanks that works