1 . 如图,在直角梯形
中,
,
,且
为
的中点,
,
分别是
,
的中点,将三角形=
沿
折起,则下列说法正确的是_____________ .(写出所有正确说法的序号)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/10/31/d9b80ef5-a186-4385-b0aa-8c3e76f4b7e2.png?resizew=233)
①不论
折至何位置(不在平面
内),都有
平面
;
②不论
折至何位置(不在平面
内),都有
;
③不论
折至何位置(不在平面
内),都有
;
④在折起过程中,一定存在某个位置,使
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/479bb5e937f4fdb1fcbca229e62e0e80.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0c05986ad5fa244bc1aedf7b5d216544.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9d78abbad68bbbf12af10cd40ef4c353.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ac047e91852b91af639feec23a9598b2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/54a5d7d3b6b63fe5c24c3907b7a8eaa3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/85c4bdfb0db1e31e8459df1d15f9ab55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b9a32bd7a1b78b5a0ec562c4025aea8c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/68a83fdd2ba72a2dba0b6b10bb3e06b9.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/10/31/d9b80ef5-a186-4385-b0aa-8c3e76f4b7e2.png?resizew=233)
①不论
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7592c4f01c8e06c7ee90df5b9413a9f5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/678b28fddb166d90878d24d6e5481080.png)
②不论
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/13c4a875c62b36bcc95d629b780d8ed4.png)
③不论
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7605ce6f221ce8cad191da0f84a216d0.png)
④在折起过程中,一定存在某个位置,使
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/29f7f37289eeb9721a6f3cbfd0d7708a.png)
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