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大多數人最為熟悉的數有兩種,即正數(+5,+17.5)和負數(-5,-17.5).負數是在中世紀出現的,它用來處理3-5這類問題.從古代人看來,要從三個蘋果中减去五個蘋果似乎是不可能的.但是,中世紀的商人卻已經清楚地…
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