一又二分之一减二又六分之五加三又十二分之一减四又十九分之二十加五又三十分之一减六又四十二分之四十一加七又五十六分之一减八

(1+1/2)-(2+5/6)+(3+1/12)-(4+19/20)+(5+1/30)-(6+41/42)+(7+1/56)-(8+71/72)+(9+1/90) =(1+1/2)-(3-1/6)+(3+1/12)-(5-1/20)+(5+1/30)-(6-1/42)+(7+1/56)-(9-1/72)+(9+1/90) =1+1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90 =1+1/2+1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1/(8*9)+1/(9*10) =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 =19/10