C(n+1,n)*C(n,n-2)
=C(n+1,1)*C(n,2)
=(n+1)*n*(n-1)/2
=(n^2-1)n/2
=(n^3-n)/2标题我写错了 是C(n,n+1)*C(n-2,n) C上标N下标N+1乘C上标N-2下标N要不你的题目错了，要不你写错了C的上标一定小于或等于下标　nn-2C n+1 * Cn 题目是这样的麻烦您了帮个忙这就对了C(n+1,n)*C(n,n-2)=C(n+1,1)*C(n,2)=(n+1)*n*(n-1)/2=(n^2-1)n/2=(n^3-n)/2就是我这样写