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:這是一道等差數列題1-3+5-7+9-11+…+97-99原式=(1+5+9+…+97)-(3+7+11+99)=(1+97)×25×1/2-(3+99)×25×1/2=100×25×1/2-102×25×1/2=(98-102)×25×1/2=-50項數=(末項-首項)÷公差+1總和=(末項…
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