Answer
y = (x+h)^{3}/h gets closer to y = 3x^{2} as h gets smaller and smaller.
Work Step by Step
The graphs are shown below for h = 2,1,0.5.
The function y = 3x^{2} is the derivative of the function y = x^{3} so that
3x^{2} = \lim\limits_{h \to 0}(x+h)^{3}/h