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[几何] 正八面体的平行于它的一个面的截面的周长为定值

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hbghlyj posted 2024-11-12 17:57 |Read mode
Modern pure solid geometry第24页第24题:
正八面体的平行于它的一个面的截面的周长为定值,等于它的各面的周长。

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original poster hbghlyj posted 2024-11-12 18:02
  1. plane=InfinitePlane[{0,0,0.25},{{-1,1,0},{1,0,-1}}];
  2. Graphics3D[{{Opacity[0.5],PolyhedronData["Octahedron","Faces"]},{Opacity[0.8],Blue,plane}},Boxed->False,Axes->False]
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.png
  1. plane=InfinitePlane[{0,0,0.5},{{-1,1,0},{1,0,-1}}];
  2. Graphics3D[{{Opacity[0.5],PolyhedronData["Octahedron","Faces"]},{Opacity[0.8],Blue,plane}},Boxed->False,Axes->False]
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original poster hbghlyj posted 2024-11-12 18:39
$\triangle DGD_1\cong\triangle D_1G'D\implies D_1G=DG'\implies D_1C_1+D_1B_1=DF\implies 3(D_1C_1+D_1B_1)=3DF$

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original poster hbghlyj posted 2024-11-12 18:42
正六面体的平行于它的一个面的截面的周长也为定值。
除正六、八面体外,还有其他多面体满足这个“平行于它的一个面的截面的周长为定值”的性质吗?

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