1/2+1/6+1/12+1/20+......1/110=1/(1*2)+1/(2*3)+1/(3*4)+1/(4*5)+....+1/(10*11)=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+........+1/10-1/11=1-1/11=10/11 不懂可追问满意请采纳谢谢
