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
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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
∵1/[(x-1)x(x+1)]
=[(x+1)-(x-1)]/[2(x-1)x(x+1)]
=1/[2x(x-1)]-1/[2x(x+1)]
=[x-(x-1)]/[2x(x-1)]-[(x+1)-x]/[2x(x+1)]
=(1/2)[1/(x-1)-1/x]-(1/2)[1/x-1/(x+1)]
=(1/2)[1/(x-1)-2/x+1/(x+1)],
∴依次令上述等式中的x为12、13、14,可依次得:
1/(11×12×13)=(1/2)(1/11-2/12+1/13),
1/(12×13×14)=(1/2)(1/12-2/13+1/14),
1/(13×14×15)=(1/2)(1/13-2/14+1/15),
将上述三个等式左右分别相加,得:
1/(11×12×13)+1/(12×13×14)+1/(13×14×15)
=(1/2)(1/11-1/12-1/14+1/15)
=(1/2)[(12-11)/(11×12)-(15-14)/(14×15)]
=(1/2)[1/(11×12)-1/(14×15)]
=(1/12)[1/(11×2)-1/(7×5)]
=(1/12)(1/22-1/35)
=(1/12)(35-22)/(22×35)
=(1/12)×[13/(11×70)]
=13/(12×770)
=13/9240
[170+1 /12] ×1 /13+11 /12
|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?
有简便方法计算:|1/11-1/12|+|1/12-1/13|+|1/14-1/13|
1/11+1/12+1/13+1/14.+1/20
巧算24点1,11,12,13
1 11 12 13算24点
1+10+11+12+13+14+15
11 12 13 14 1要理由
(170+1/12)×1/13+11/12简便运算
1/13+2/13+3/13+4/13+5/13+6/13+7/13+8/13+9/13+10/13+11/13+12/13
11-13分之12-13分之1等于几?
13分子1+13分子2+13分子3``````+13分子11+13分子12+13分子11``````+13分子3+13分子2+13分子1快
|1/11-1/10|+|1/12-1/11|+|1/13-1/12|-|1/13-1/10|=?
12 13 1 2
91*1/13-1/13*100+9*1/13+1111/12/11
{1/12+(-1/11)}+{1/13+(-1/12)}+{1/14+(-1/13)}+{1/15+(-1/14)}怎么算
-1/10*11+1/11*12+1/12*13+1/13*14+···1/19*20的值