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

来源：百度知道编辑：UC知道时间：2024/06/08 19:46:56

要用简便方法做哦

1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72
=1-1/2+1/2-1/3+1/3-1/4+……＋1/8-1/9
＝1-1/9
＝8/9

原式=1/(1*2+)+1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)+(7*8)+1/(8*9)
=1-1/2+1/2-1/3+1/3......-1/7+1/7-1/8+1/8-1/9
＝1-1/9
＝8/9
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(1/2) (1/4+1/6)= 1/2 ，1/3 ,1/6 /1/6 ,() 1/2+1/6+1/12+1/20+1/30 1/2+1/4+1/6+1/8+.......+1/n=? -1/2-1/6-1/12-1/20-``````````````-1/4026042 1/2+1/6+1/12+......+1/1980+1/2070=? 1/2 1/6 1/3 2 ( ) 3 1/2 数字推理 1/2*4+1/4*6+1/6*8+.......+1/2006*2008 1/2*4+1/4*6+1/6*8+1/48*50 1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=