摘要：忘了二项式定理！！！ \[(x+y)^{\overline{n}} = \sum \dbinom{n}{i}x^{\overline{i}}y^{\overline{n-i}} \]证明：\(\displaystyle \text{R.H.S.} = n!(-1)^n \sum \dbinom{-x 阅读全文