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简便计算：2×3+3×4+4×5+…+17×18，无从下手，原来有这个规律
简便计算：2×3+3×4+4×5+…+17×18，无从下手，原来有这个规律
初中数学，有理数混合运算，简便计算，基础训练，培优专题328/395
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