1+1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/110等于几!要具体的办法,别给我通分!

1+1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/110 =1+(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+(1/7-1/8)+(1/8-1/9) )+(1/9-1/10) +(1/10-1/11) =2-1/11 =21/11