20-(2|3+2|15+2|56+2|72+2|99)怎么做

注：2/n(n+2)=1/n-1/(n+2)感觉题目好像错了,理论上原题应该是20-(2|3+2|15+2|35+2|63+2|99)=20-(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11）=20-(1-1/11)=20-10/11=210/11类似该题的有1/2+1/6+1/12+。。。+1/n(n+1)=n/(n+1)1/n(n+1)=1/n-1/(n+1)