Hey guy wondering if someone could help me out here.

I need to find a formula for the slope of the tangent line to the graph offat a general point x=xknot

and then use the formula obtained in first part to find the slope of the tangent line for the given value of xknot... heres the function f(x)=$\displaystyle \frac{1}{\sqrt{x}} $ ; xknot=4

I'm having trouble with the initial setup...