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1/6+1/12+1/20+1/30+1/42+1/56+1/72等于多少?
题目详情
1/6+1/12+1/20+1/30+1/42+1/56+1/72等于多少?
▼优质解答
答案和解析
1/6+1/12+1/20+1/30+1/42+1/56+1/72
1/2*3+1/3*4+1/4*5+1/5*6+1/6*7+1/7*8+1/8*9
=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
=1/2-1/9
=(9-2)/18
=7/18
1/2*3+1/3*4+1/4*5+1/5*6+1/6*7+1/7*8+1/8*9
=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
=1/2-1/9
=(9-2)/18
=7/18
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