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1/12*13+1/13*14+.+1/19*20的值为?为什么

1/12*13+1/13*14+.+1/19*20 =(1/12-1/13)+(1/13-1/14)+。。。+(1/19-1/20) =1/12-1/20 =(5-3)/60 =1/30

1/(12*13)=1/12-1/13 1/(13*14)=1/13-1/14 分母同分,分子一减等于1,以此类推 原式=1/12-1/13+1/13-1/14 +.....+1/19-1/20 =1/12-1/20 =1/30

解: 1/10*11+1/11*12+1/12*13+1/13*14+1/14*15 =1/10-1/11+1/11-1/12+1/12-1/13+1/13-1/14+1/14-1/15 =1/10-1/15 =3/10-2/30 =1/30 祝你开心

整数部分是 0

10.1+11.11+12.12+13.13+14.14+……+19.19 =10+11+12+13+……+19+0.1+0.11+0.12+……+0.19 =(10+19)×10/2+(0.1+0.19)×10/2 =145+1.45 146.45

|1/12-1/11|+|1/13-1/12|+|1/14-1/13| =1/11-1/12+1/12-1/13+1/13-1/14 =1/11-1/14 =14/154-11/154 =3/154 =154分之3 朋友,请采纳正确答案,你们只提问,不采纳正确答案,回答都没有劲!!! 朋友,请【采纳答案】,您的采纳是我答题的动力,如...

0.66877140317543

10*1/19

1/(12×13)+1/(13×14)+1/(14×15)。。。+1/(19×20) =1/12-1/13+1/13-1/14+……+1/19-1/20 =1/30 解题技巧是:(一个公式!记住啦!) 1/n*(n+1)=1/n-1/(n+1) 按这样的公式把各项拆开,再把中间的全部约去,最后直接用第一个减去最后一个就好啦...

1/a(a+1)=1/a-1/(a+1) 1/(12*13)+1/(13*14)+1/(14*15)+1/(15*16)+1/(16*17)+1/(17*18)+1/(18*19)+1/(19*20) =1/12-1/13+1/13-1/14+1/14-1/15+……+1/19-1/12 =1/12-1/20 =5/60-3/60 =2/60 =1/15

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