1/(12×13)+1/(13×14)+……+1/(19×20)的值为:A.1/12 B.1/20 C.1/30 D.1/40一道公考题,
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1/(12×13)+1/(13×14)+……+1/(19×20)的值为:A.1/12B.1/20C.1/30D.1/40一道公考题,1/(12×13)+1/(13×14)+……+1/(19×20)的值
1/(12×13)+1/(13×14)+……+1/(19×20)的值为:A.1/12 B.1/20 C.1/30 D.1/40一道公考题,
1/(12×13)+1/(13×14)+……+1/(19×20)的值为:
A.1/12 B.1/20 C.1/30 D.1/40
一道公考题,
1/(12×13)+1/(13×14)+……+1/(19×20)的值为:A.1/12 B.1/20 C.1/30 D.1/40一道公考题,
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
=2/60
=1/30
选C
c
1/12-1/20=1/30
1/(12*13)=1/12-1/13,消去中间向即可
因为:1/(12×13)=1/12-1/13 1/(13×14)=1/13-1/14。。。。。。。1/(19×20)=1/19-1/20
也就是原式=1/12-1/13+1/13-1/14+1/14-1/15+1/15-1/16+1/16-1/17+1/17-1/18+1/18-1/19+1/19-1/20=1/12-1/20=1/30
所以答案为C
1/(12×13×14)+1/(13×14×15)+1/(14×15×16)+1/(15×16×17)
1/(12×13)+1/(13×14)+……+1/(19×20)等于多少
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