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