I need to use the formal definition of a derivative,

g'(x) = lim h->0 (f(x + h) - f(x)) / h

to solve x^(2/3)...

lim h->0 (f(x+h)^(2/3) - x^(2/3)) / h

I know the answer is obviously (2/3)x^(-1/3) but we're supposed to use the difference quotient as stated above. Any help would be greatly appreciated