2/1+6/1+12/1+20/1+30/1+42/1+56/1+72/1+90/1+110/1=?

问题描述:

2/1+6/1+12/1+20/1+30/1+42/1+56/1+72/1+90/1+110/1=?
有什么规律,怎么算的.
1个回答 分类:英语 2014-12-15

问题解答:

我来补答
(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
=(1-2/1)+(2/1-3/1)+(3/1-4/1)+(4/1-5/1)+(5/1-6/1)+(6/1-7/1)+(7/1-8/1)+(8/1-9/1)+(9/1-10/1)+(10/1-11/1)
=1-11/1
=11/10
 
 
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