你的题目写反了吧，应当是
1/2+1/6+1/12+1/20+1/30+1/56+1/72
解法如下：
1/2=1-1/2
1/6=1/2-1/3
1/12=1/3-1/4
1/20=1/4-1/5
1/30=1/5-1/6
1/42=1/6-1/7
1/56=1/7-1/8
1/72=1/8-1/9
题目答案：1/2+1/6+1/12+1/20+1/30+1/56+1/72=1-1/9=8/9
1/2+1/6+1/12+1/20+1/30+1/56+1/72
解法如下：
1/2=1-1/2
1/6=1/2-1/3
1/12=1/3-1/4
1/20=1/4-1/5
1/30=1/5-1/6
1/42=1/6-1/7
1/56=1/7-1/8
1/72=1/8-1/9
题目答案：1/2+1/6+1/12+1/20+1/30+1/56+1/72=1-1/9=8/9
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第1个回答 2020-03-05
很高兴收到你的求助，我来帮你解答吧。
解：2/1+6/1+12/1+20/1+30/1+42/1+56/1+72/1+90/1
=1/(1x2)+1/(2x3)+1/(3x4)+1/(4x5)+1/(5x6)+1/(6x7)+1/(7x8)+1/(8x9)+1/(9x10)
=(1-1/2+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+……+(1/8-1/9)+(1/9-1/10)
=1+(1/2-1/2)+(1/3-1/3)+(1/4-1/4)+(1/5-1/5)+……+(1/8-1/8)+(1/9-1/9)-1/10
=1-1/10
=9/10
解：2/1+6/1+12/1+20/1+30/1+42/1+56/1+72/1+90/1
=1/(1x2)+1/(2x3)+1/(3x4)+1/(4x5)+1/(5x6)+1/(6x7)+1/(7x8)+1/(8x9)+1/(9x10)
=(1-1/2+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+……+(1/8-1/9)+(1/9-1/10)
=1+(1/2-1/2)+(1/3-1/3)+(1/4-1/4)+(1/5-1/5)+……+(1/8-1/8)+(1/9-1/9)-1/10
=1-1/10
=9/10
第2个回答 2022-05-07
你的题目写反了吧，应当是
1/2+1/6+1/12+1/20+1/30+1/56+1/72
解法如下：
1/2=1-1/2
1/6=1/2-1/3
1/12=1/3-1/4
1/20=1/4-1/5
1/30=1/5-1/6
1/42=1/6-1/7
1/56=1/7-1/8
1/72=1/8-1/9
题目答案：1/2+1/6+1/12+1/20+1/30+1/56+1/72=1-1/9=8/9
1/2+1/6+1/12+1/20+1/30+1/56+1/72
解法如下：
1/2=1-1/2
1/6=1/2-1/3
1/12=1/3-1/4
1/20=1/4-1/5
1/30=1/5-1/6
1/42=1/6-1/7
1/56=1/7-1/8
1/72=1/8-1/9
题目答案：1/2+1/6+1/12+1/20+1/30+1/56+1/72=1-1/9=8/9
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