不知道你学过“阶乘”没有?!
1×2×3×……×(n-1)×n=n!
按照题目所给的提示,分母分别为(n+1)!
这样,各项就是n/(n+1)!=[(n+1)-1]/(n+1)!
=[(n+1)/(n+1)!]-[1/(n+1)!]
=(1/n!)-[1/(n+1)!]
所以,原式=[1-(1/2!)]+[(1/2!)-(1/3!)]+……[(1/5!)-(1/6!)]
=1-(1/6!)
=1-(1/1×2×3×4×5×6)
=719/720
追问没有学过阶乘,看不懂!过程能再简单吗,要能看得懂的?