1*(1/2)=1-(1/2)
(1/2)*(1/3)=(1/2)-(1/3)
……
(1/39)*(1/40)=(1/39)-(1/40)
将它们相加就出现中间项相互抵消,得出第一项和最后一项
即1-(1/40)=39/40
1/1x2/1+2/1x3/1+3/1x4/1+4/1x5/1...+39/1x40/1怎么算还有过程
2个回答
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