解题方法
1 . 如图,在正方体
中,
为棱
上的动点,
平面
为垂足.给出下列四个结论:
;
②线段
的长随线段
的长增大而增大;
③存在点
,使得
;
④存在点
,使得![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7a5f1641947153c80b987320885a2b57.png)
平面
.
其中所有正确结论的序号是__________ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6e09725691ee7851f54c0dee86b2bf55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dad2a36927223bd70f426ba06aea4b45.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f1c982eb645d77aa24c642fca6d72e10.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8c49adfabb11c35a6e72cde3af1483b6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c82cbb7fec64ae746256923b1a9479c9.png)
②线段
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3525ddc5153fada64eaf14e50b536542.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20a541b81584a032f571159ea152c85a.png)
③存在点
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dad2a36927223bd70f426ba06aea4b45.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8d643e10124279e8863fe3e21cba688b.png)
④存在点
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dad2a36927223bd70f426ba06aea4b45.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7a5f1641947153c80b987320885a2b57.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/895d6f710d5f67e1d4c7408d50d77281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/048e39e4ac8a62a129b6816dd18902ea.png)
其中所有正确结论的序号是
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