xn―=∑i=0n[ni](−1)n−ixi 证明: xn+1―=(x−n)xn―=(x−n)∑i[ni](−1)n−ixi=∑i[ni](−1)n−ixi+1−n∑i[ni](−1)n−ixi=∑i[ni−1](−1)n+1−ixi+n∑i[ni](−1)n+1−ixi=∑i([ni−1]+n∗[ni])(−1)n+1−ixi=∑i[n+1i]...