Because f(x) = x 9+ax 8+bx 7+~+MX+n, f'(0)=m, and m is the first-order coefficient of f (x). F (x) = (X-0) (x-a1) ... (x-A8), x is regarded as x-0, each of the nine brackets gives x or a constant, while the principal term gives x a bracket, the other brackets give constants, and 0 is multiplied by any number, so the principal term is still a/kloc-0.