1/12*13+1/13*14+.......+1/19*20
来源:百度知道 编辑:UC知道 时间:2024/06/15 04:44:45
求和(n=12到19):1/(n*(n+1)) 共有8项
1/(n*(n+1))=1/n-1/(n+1)
也就是:(1/12-1/13)+(1/13-1/14)......+(1/19-1/20)
打开括号:1/12-1/20=1/30
答案为:1/30
我猜你问的是1/(12*13)吧?1/12*13=13/12了,可以直接表示的
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
=1/30
1/12*13+1/13*14+.......+1/19*20
=1/13(1/12+1/14)+......1/19(1/18+1/20)
=1/(6*14)+1/(7*16)+1/(8*18)+1/(9*20)
=1/(6*14)+1/(14*8)+1/(8*18)+1/(18*10)
=1/14(1/6+1/8)+1/18(1/8+1/10)
=1/(6*8)+1/(8*10)
=1/8(1/6+1/10)
=1/30
1/12*13+1/13*14+.......+1/19*20
=1/13(1/12+1/14)+......1/19(1/18+1/20)
=1/(6*14)+1/(7*16)+1/(8*18)+1/(9*20)
=1/14(1/6+1/8)+1/18(1/8+1/10)
=1/(6*8)+1/(8*10)
=1/30
1/11+1/12+1/13+1/14+1/15=?
1/12*13+1/13*14+.......+1/19*20
1/(12×13)+1/(13×14)+1/(14×15)。。。+1/(19×20)=?
比较大小:1/11+1/29 1/12+1/25 1/13+1/21 1/14+1/19
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1/(12×13)+1/(13×14)+……+1/(19×20)=???
已知1-1/2=1/2 1/2-1/3=1/6 1/3-1/4=1/12 那么1/6-1/7=()1/12-1/13=()1/2+1/6+1/12=()
1/1*2+1/2*3+1/3*4+1/4*5+1/5*6+1/6*7+1/7*8+1/8*9+1/9*10+1/10*11+1/11*12+1/12*13+1/13*14+1/14*15=?