1/(12*13)+1/(13*14)+1/(14*15)+1/(15*16)+1/(16*17)+1/(17*18)+1/(18*19)+1/(19*20)=?
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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*13)+1/(13*14)
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*13)+1/(13*14)+1/(14*15)+1/(15*16)+1/(16*17)+1/(17*18)+1/(18*19)+1/(19*20)=?
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/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
=(1/12-1/13)+(1/13-1/14)+...+(1/19-1/20)
=1/12-1/20
=1/30
化简=1/12-1/13+1/13-1/14+1/14-1/15+..........1/18-1/19+1/19-1/20=1/12-1/20=1/30
原式=(13-12)/12*13+(14-13)13*14+——-----
=13/12*13-12/12*13+。。。。。。
=1/12-1/13+。。。。。。。+1/19-1/20
=1/12-1/20
=(5-3)/60
=1/30
|1/11-1/12|+|1/12-1/13|+|1/13-1/14+|1/14-1/15|
1/10*11+1/11*12+1/12*13+1/13*14+1/14*15等于?
1+10+11+12+13+14+15
11 12 13 14 1要理由
有简便方法计算:|1/11-1/12|+|1/12-1/13|+|1/14-1/13|
1/11*12*13+1/12*13*14+1/13*14*15等于多少?1/11*12*13+1/12*13*14+1/13*14*15,急用,最好带上每一步意思
奥数1/(11×12×13)+1/(12×13×14)+1/(13×14×15)=的解题思路
{1/12+(-1/11)}+{1/13+(-1/12)}+{1/14+(-1/13)}+{1/15+(-1/14)}怎么算
1/12*13 1/13*14 1/14*15 .1/19*20()1/12*13+1/13*14+1/14*15+.+1/19*20()1/2+1/1/12+1/20+1/30+1/42()详细步骤
比较12分之1,13分之12,-14分之13,-15分之14的大小
1/10*11+1/11*12+1/12*13+1/13*14+1/14*15等于?我看不懂
1/(12×13×14)+1/(13×14×15)+1/(14×15×16)+1/(15×16×17)
|13分之1-12分之1|+|14分之1-13分之1|+|15分之1-14分之1|,计算,
1/(12×13)+1/(13×14)+……+1/(19×20)等于多少
1/12*13+1/13*14+.+1/19*20的值为?为什么?
1/(12*13)+1/13*14)--1/(19*20)值=
1/(12+13)+1/(13+14)+.+1/(19+20)=
丨1/11-1/12丨+丨1/12-1/13丨+丨1/14-1/13丨等于多少