a n = ∑ k = 0 n C n k b k a_n=\sum\limits_{k=0}^nC_{n}^{k}b_k an=k=0∑nCnkbk 可以得到 b n = ∑ k = 0 n C n k a k ( − 1 ) n − k b_n=\sum\limits_{k=0}^nC_{n}^{k}a_k(-1)^{n-k} bn=k=0∑nCnkak(−1)n−k 做题!