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胖博士今天分享的题目如下: (1+0.12+0.23)×(0.12+0.23+0.34)-(1+0.12+0.23+0.34)×(0.12+0.23)(2014年第三届海峡杯五年级决赛第9题) 分析:=(1+0.12+0.23)×(0.12+0.23+0.34)-(1+0.12+0.23)×(0.12+0.23)-0.34×(0.12+0.23) =(1+0.12+0.23)×(0.12+0.23+0.34-0.12-0.34)-0.34×(0.12+0.23) =0.34 太复杂了怎么办?换元法, 设1+0.12+0.23=A,0.12+0.23+0.34=B 则原式=A×B-(A+0.34)×(B-0.34) =AB-(AB+0.34B-0.34A-0.342) =AB-AB+0.34(A-B+0.34) =0.34×(1+0.12+0.23-0.12-0.23-0.34+0.34) =0.34×1 =0.34 视频讲解参见 大家可以做完后再看解答哦。 |
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