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悠闲数学娱乐论坛(第3版)
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立体几何一题
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realnumber
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Post time 2015-1-26 10:25
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Post time 2015-1-26 10:28
本帖最后由 realnumber 于 2015-1-26 10:35 编辑
1.$2\sqrt{2}$
2.设BC中点M,AD中点N,
那么有O到AD距离小于等于$\abs{OM}+\abs{MN}$
可得取等时，最大，此时BN在面α上射影长度为$2\sqrt{3}\cos{(∠NBC-45\du)}=2+\sqrt{2}$，AD射影长度为4,所以面积为$4+2\sqrt{2}$
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2025-3-5 12:14 GMT+8
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