裂项求和即可
2/1+6/1+12/1+20/1+30/1+...+110/1
=(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+.+(1/10-1/11)
=1-1/11
=10/11