
-2分之1+6分之1+12分之1+30分之1+42分之1=多少 计算 要过程
展开全部
-1/2+1/6+1/12+1/30+1/42
=-1/2+(1/2-1/3)+(1/3-1/4)+(1/5-1/6)+(1/6-1/7)
=-1/2+1/2-1/3+1/3-1/4+1/4+1/5-1/6+1/6-1/7
=1/5-1/7
=2/35
=-1/2+(1/2-1/3)+(1/3-1/4)+(1/5-1/6)+(1/6-1/7)
=-1/2+1/2-1/3+1/3-1/4+1/4+1/5-1/6+1/6-1/7
=1/5-1/7
=2/35
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