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12/1+20/1+30/1+``````+90/1分子规律是+8+10+12+14+16+18++++++++++++++·········
题目详情
12/1+20/1+30/1+``````+90/1
分子规律是+8+10+12+14+16+18++++++++++++++·········
分子规律是+8+10+12+14+16+18++++++++++++++·········
▼优质解答
答案和解析
12/1+20/1+30/1+``````+90/1
=3/1-4/1+4/1-5/1+5/1-6/1+……+9/1-10/1
=3/1-10/1
=30/7
=3/1-4/1+4/1-5/1+5/1-6/1+……+9/1-10/1
=3/1-10/1
=30/7
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