What are the steps to find the derivitive of a function, such as:
f(x) = x3 - 9x + 8
i know the formula is f(x)-f(x)/x-a
but idk how to use it
The correct formula is $\displaystyle \lim_{x\to a}\frac{f(x)- f(a)}{x-a}$. That is not at all what you wrote. In the first place, you don't have a limit. In the second, you have "- f(x)" instead of "f(a)". And finally, "f(x)- f(x)/x-a", without parentheses, means $\displaystyle f(x)- \frac{f(x)}{x}- a$"
In any case, you need to find
$\displaystyle \lim_{x\to a}\frac{x^3- 9x-8- (a^3- 9a- 8)}{x-a}= \lim_{x\to a}\frac{x^3-a^3- 9(x- a)}{x-a}$
If you use the fact that $\displaystyle x^3- a^3= (x-a)(x^2+ x+ 1)$ that will be fairly easy.