求Sn=C(n,1)+2C(n,2)+...+nC(n,n)C(n,1)+2C(n,2)+...+nC(n,n) n是下标
问题描述:
求Sn=C(n,1)+2C(n,2)+...+nC(n,n)
C(n,1)+2C(n,2)+...+nC(n,n) n是下标
答
一,n为奇数,Sn=nC(n,n)+(1+n-1)C(n,1)+(2+n-2)C(n,2)+…+nC(n,n-1/2)=n[C(n,0)+C(n,1)+…+C(n,n-1/2)=n*2de(n-1)次方 二,n为偶数,Sn也一样