Hanah's (symmetrical difference) definition of the derivative;

$f'(x)=\lim_{h\rightarrow 0}\frac{f(x+h)-f(x-h)}{2h}$

f(x) = x² − 3

Find f '(x), which is also the value of the limit.

Power Rule
if f(x) = xⁿ
then f '(x) = nx^{n − 1}

f(x) = x² − 3
f '(x) = __________