1/3+1/6+1/10+1/15+1/21+…1/55
问题描述：
1/3+1/6+1/10+1/15+1/21+…1/55
答
1/3+1/6+1/10+1/15+1/21+…1/55
=2*(1/6+1/12+1/20+1/30+1/42+…1/110)
=2*[(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+.+(1/10-1/11)]
=2*[1/2-1/11]
=1-2/11
=9/11