六减二分之三减六分只七减十二分之十三减二十分之二十一减三十分之三十一,等于多少.

6-3/2-7/6-13/12-21/20-31/30=6-(1+1/2)-(1+1/6)-(1+1/12)-(1+1/20)-(1+1/30)=6-1-1/2-1-1/6-1-1/12-1-1/20-1-1/30=-(1/2+1/6+1/12+1/20+1/30)=-[(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)]=-[1-1/2+1/2-1/3...