在《九章算术·商功》中将四个面均为直角三角形的三棱锥称为鳖臑(biē nào),在如下图所示的鳖臑
中,
,
,
,则△
的直角顶点为______ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ddfe0ccf24d760c77535a70c92dad145.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/adc969fe7eab49a6e9e2575386b7b3c4.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ba32ea6d45d74abf20ebfe77a866e58a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1a2fc51de957401a6193689497e6014d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1e582d73b96ba649378379c3074d506d.png)
![](https://img.xkw.com/dksih/QBM/2020/2/18/2401669017673728/2401756928507905/STEM/62babb89df3743e79c58c150ce52e871.png?resizew=170)
更新时间:2020-02-18 17:29:53
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【知识点】 证明线面垂直
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解题方法
【推荐1】如图,已知在矩形
中,
,点
是边
的中点,
与
相交于点
,现将
沿
折起,点
的位置记为
,此时
,则二面角
的余弦值为__________ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0cd4fb83908d0cabf3cc17ea6ce4a3c5.png)
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【推荐2】
,
是两条异面直线,它们成
角,
,
是
上的点,
,
是
上的点,
,
.若
,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/84218fb0e55baa90f8179601b41d7b31.png)
________ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/996bf3d35b6763cbc1a423b13a9df2dd.png)
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7f9e8449aad35c5d840a3395ea86df6d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a18722354086c42e62334983fc50eb6a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/97c01fdc7bc471af0b264a04aef0823e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2d7ed7f746c3314bbb402f0a90cbdace.png)
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【推荐3】如图,直角梯形
中,![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a9bfa68259d7a331be323b2038d628a.png)
为
的中点,以
为折痕将
折起,使点
到达点
的位置,且
,则
到平面
的距离为__________ ;PC与平面
所成角的余弦值为__________ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a9bfa68259d7a331be323b2038d628a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3c80a79eddc9dfdf341f2cd3af710cb9.png)
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