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3个回答
展开全部
第一题:
1又1/4-9/20+11/30-13/42+15/56-17/72+19/90
=1+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+1/10
=11/10
1又1/4-9/20+11/30-13/42+15/56-17/72+19/90
=1+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+1/10
=11/10
追答
第二题:1-1/6+1/42+1/56+1/72+1/90
=1-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10
=1-1/10
=9/10
追问
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