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3/2-5/6+7/12-9/20+11/30-13/42+15/56-17/72+19/90...急
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3/2-5/6+7/12-9/20+11/30-13/42+15/56-17/72+19/90...急
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答案和解析
3/2-5/6+7/12-9/20+11/30-13/42+15/56-17/72+19/90
=1+1/2-(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)+1/9+1/10
=1+1/2-1/2-1/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7+1/7+1/8-1/8-1/9+1/9+1/10
=1+1/10
=11/10
=1+1/2-(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)+1/9+1/10
=1+1/2-1/2-1/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7+1/7+1/8-1/8-1/9+1/9+1/10
=1+1/10
=11/10
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