f(x)是x的多项式,fm'(x)是f(x)的m阶导数
f(a)=f'(a)=0,f''(a）≠0,f(a)有二重重根
f(a)=f'(a)=f''(a)=..=fm'(a)=0,fm'(a)≠0,f(a)有m重重根