Let the function :

$$
f(x) =x^{3}-3x
$$ with its domain in the real numbers.

Determine with the help of
$$
f'(x) \equiv \lim \_{h\rightarrow 0}\dfrac{f\left( x+h\right) -f\left( x\right) }{h}
$$

the derivative $f'$ of function $f$.

I tried to plug the values of $f$ inside of $f'$:

$$
f (x ) =\lim \_{h \to 0}\frac{(x+h)^{3}-3(x+h) -(x^{3}-3x) }{h}
$$

I then tried to factorize but it didn't yeld results.

I don't understand how I can expand $(x + h)^3$ properly.