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解题方法
1 . 《九章算术·商功》:“斜解立方,得两堑堵.斜解堑堵,其一为阳马,一为鳖臑.阳马居二,鳖臑居一,不易之率也.合两鳖臑三而一,验之以棊,其形露矣.”刘徽注:“此术臑者,背节也,或曰半阳马,其形有似鳖肘,故以名云.中破阳马,得两鳖臑,鳖臑之起数,数同而实据半,故云六而一即得.”
![](https://img.xkw.com/dksih/QBM/editorImg/2022/11/27/e5993170-2f4e-4cc5-b942-25e82698d51b.png?resizew=444)
如图,在鳖臑ABCD中,侧棱
底面BCD;
![](https://img.xkw.com/dksih/QBM/editorImg/2022/11/27/a607565f-9b51-4909-854f-36d57edfe0e2.png?resizew=340)
(1)若
,
,
,
,求证:
;
(2)若
,
,
,试求异面直线AC与BD所成角的余弦.
(3)若
,
,点P在棱AC上运动.试求
面积的最小值.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/11/27/e5993170-2f4e-4cc5-b942-25e82698d51b.png?resizew=444)
如图,在鳖臑ABCD中,侧棱
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/21f9157fce2a8339d281178c7c0bccbe.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/11/27/a607565f-9b51-4909-854f-36d57edfe0e2.png?resizew=340)
(1)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4bd6a2b112facda441f4e34bf5c145fa.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/00be7c72b7d222730571ce5d7c288eba.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8c125d80008eed00b5bf47dc5df47246.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e468b7ccc9795b5feb53ad072e597b34.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/78f2b8dcbb2f7c2047896bc7aecc22bf.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ced06b71073e1bb777f326f06016ce17.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ef0402dd5ae3db10281f9f1e11738bcb.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/037b342a682cbd4241855a243da3c016.png)
(3)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ff9c7cbcc38b28d45c8539710e5b260a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a2e1ab67f8e48ad3340cf9d165cd75f0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/acee03d4bb4667b6c345221b6c9b0fa4.png)
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