2n/(n+1)n!
问题描述:
2n/(n+1)n!
答
2n/(n+1)!化成2【1/n!-1/(n+1)!】会吗(n+1)n!=(n+1)!
1/n! = (n+1)/(n+1)!
2n/(n+1)n!
=2[n/(n+1)n!]
=2{ [n+1/(n+1)n! ]-[1/(n+1)n!] }
=2[1/n!-1/(n+1)!]
符号有些繁琐,耐心一点看,这样说应该可以吧。