■サマーヴィルの等面四面体(その568)

△3

  P0(0,0,0)

  P1(0,0,3h)

  P2(m/√2,m√3/√2,2h)

  P3(2m/√2,0,h)

とおくと

  P0P1^2=9h^2

  P0P2^2=2m^2+4h^2

  P0P3^2=2m^2+h^2

  P1P2^2=2m^2+h^2

  P1P3^2=2m^2+4h^2

  P2P3^2=2m^2+h^2

2m^2+h^2(3)<2m^2+4h^2(2)

9h^2(1)

ここで,

  9h^2=2m^2+h^2,m^2=4h^2

ならば△3

  P0P1^2=9h^2

  P0P2^2=9h^2

  P0P3^2=12h^2

  P1P2^2=12h^2

  P1P3^2=9h^2

  P2P3^2=9h^2

△3は

  P0P1=P1P2=P2P3=√3

  P0P2=P1P3=2

  P0P3=√3

9h^2=3,h^2=1/3,m^2=4/3

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 △4は

  P0P1=P1P2=P2P3=P3P4=2

  P0P2=P1P3=P2P4=√6

  P0P3=P1P4=√6

  P0P4=2

であるから

  3m^2+h^2=16h^2=4

  3m^2+9h^2=4m^2+4h^2=6

h^2=1/4,m^2=5/4

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△5は

  P0P1=P1P2=P2P3=P3P4=P4P5=√5

  P0P2=P1P3=P2P4=P3P5=√8

  P0P3=P1P4=P2P5=3

  P0P4=P1P5=√8

  P0P5=√5

4m^2+h^2(5)<4m^2+16h^2(2)

6m^2+4h^2(4)<6m^2+9h^2(3)

25h^2(1)

4m^2+h^2=5,4m^2+16h^2=8

6m^2+4h^2=8,6m^2+9h^2=9

25h^2=5

h^2=1/5,m^2=6/5

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△6は

  P0P1=P1P2=P2P3=P3P4=P4P5=P5P6=√6

  P0P2=P1P3=P2P4=P3P5=P4P6=√10

  P0P3=P1P4=P2P5=P3P6=√12

  P0P4=P1P5=P2P6=√12

  P0P5=P1P6=√10

  P0P6=√6

5m^2+h^2(6)<5m^2+25h^2(2)

8m^2+4h^2(5)<8m^2+16h^2(3)

9m^2+9h^2(4)

36h^2(1)

5m^2+h^2=6,5m^2+25h^2=10

8m^2+4h^2=10,8m^2+16h^2=12

9m^2+9h^2=12

36h^2=6

h^2=1/6,m^2=7/6

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[1]n=3の本体

  9h^2=2m^2+h^2=3,h^2=1/3,m^2=4h^2=4/3

[2]n=4の本体

  16h^2=3m^2+h^2=4,h^2=1/4,m^2=5h^2=5/4

[3]n=5の本体

  25h^2=4m^2+h^2=5,h^2=1/5,m^2=6h^2=6/5

[まとめ]最短辺の長さは√nであるから,

  h^2=1/n,m^2=1+1/n

  nh=√n  (最短辺の方向)

これは△in △,non△ in non△に共通している.ただし,non△ in non△では等間隔ではない.

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