A function f(x)in a neighborhood of x 0 is second order continuous differentiable,andf(O)≠0，f'(O)≠0，f"(O)≠0.To prove:there is only A set of real Numbers A1,2,23 makes when h→0，入1f(h)+入2f(2h)+入3f(3h)-f(0)is higher than ha2order infinitesimal.