名校
解题方法
1 . 在正方体
中,
分别为棱
的中点,现在顶点
处截去三棱锥
,仿此同样方式,在顶点
处各截去三棱锥,设剩下的几何体为
,
(1)几何体
是几面体?共有多少条棱?(直接写出结论,不需要说明理由)
(2)若正方体的棱长为
,求几何体
的表面积;
(3)若
分别为
的中点,求平面
与面
所成二面角的正弦值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6e09725691ee7851f54c0dee86b2bf55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5b094411c562930ff2d67b582cfd48cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/68965a6791bdeeff6e906ce7b3d2e3b3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/35e7db19157a90647f1f1e9bc7b9a7ab.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1f2e7a61c834e6cd5c8ff37862d3921f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0cb9ad1e34877b0db02d0219332b0f7b.png)
(1)几何体
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0cb9ad1e34877b0db02d0219332b0f7b.png)
(2)若正方体的棱长为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/61128ab996360a038e6e64d82fcba004.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0cb9ad1e34877b0db02d0219332b0f7b.png)
(3)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ebe1aed936e231d7824c6ac1feeb0326.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9b2070d3881b08d3e4405a0981d44854.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ed4cba9d2412e4a28f8740bddd5738d4.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1c0ca8f9bf2190154e4695aa666f57be.png)
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