三又九分之五和二又十五分之八怎么通分？

数学1又2分之1减2又6分之5加

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

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