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集合题有时用维恩图更简单。
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沙发#
发布于：2015-09-18 18:41
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![20天大作战[2015]](https://bbs.jd100.com/attachment/medal/cec543c13f7ea1b.jpg "20天大作战[2015]"){kind=small}
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板凳#
发布于：2015-09-19 13:34
what？
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地板#
发布于：2015-09-20 19:28
维恩图神马东东
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4楼#
发布于：2015-09-22 21:11
有些就得画数轴，数形结合其实是数学的常规方法，很多题用这个方法会更简单
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![7天勇士[春]](https://bbs.jd100.com/attachment/medal/7b734d35544b9d3.png "7天勇士[春]"){kind=small}
![21天勇士[春]](https://bbs.jd100.com/attachment/medal/557cbed59379b9b.png "21天勇士[春]"){kind=small}
![14天勇士[春]](https://bbs.jd100.com/attachment/medal/0a2a8be87813938.png "14天勇士[春]"){kind=small}
![28天勇士[春]](https://bbs.jd100.com/attachment/medal/13d5b846139de25.png "28天勇士[春]"){kind=small}
![7天勇士[寒]](https://bbs.jd100.com/attachment/medal/3ae915c994fd934.jpg "7天勇士[寒]"){kind=small}
![14天勇士[寒]](https://bbs.jd100.com/attachment/medal/9aacf8cc0ea8134.jpg "14天勇士[寒]"){kind=small}
![21天勇士[寒]](https://bbs.jd100.com/attachment/medal/cda474e823b15b8.jpg "21天勇士[寒]"){kind=small}
![28天勇士[寒假]](https://bbs.jd100.com/attachment/medal/f7cb21a2bdf0790.jpg "28天勇士[寒假]"){kind=small}
![勇不止步[夏]](https://bbs.jd100.com/attachment/medal/d81a441ef64b068.jpg "勇不止步[夏]"){kind=small}
![勇不止步[春]](https://bbs.jd100.com/attachment/medal/f783eb36b20a4e2.jpg "勇不止步[春]"){kind=small}
![20天大作战[2014]](https://bbs.jd100.com/attachment/medal/465e7ccd53045d5.png "20天大作战[2014]"){kind=small}
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5楼#
发布于：2015-09-24 22:08
正解啊..
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