f(x) = 4x^2 + 2
f'(x) = lim (h --> 0) (f(x +h) - f(x)) / h
f'(x) = lim (h --> 0) (4(x + h)^2 + 2 - (4x^2 + 2)) / h
f'(x) = lim (h --> 0) (4(x^2 + 2xh + h^2) + 2 - 4x^2 - 2) / h
f'(x) = lim (h --> 0) (4x^2 + 8xh + 4h^2 + 2 - 4x^2 - 2) / h
f'(x) = lim (h --> 0) (8xh + 4h^2) / h
f'(x) = lim (h --> 0) 8x + 4h = 8x
f'(3) = 8*3 = 24