■サマーヴィルの等面四面体(その379)

△3

  P0(1,0,√2)

  P1(0,0,0)

  P2(1,√2,0)

  P3(2,0,0)

  P0P1=P1P2=P2P3=√3

  P0P2=P1P3=2

  P0P3=√3

 試しに

  P0(m,0,m√2,h)

  P1(0,0,0,0)

  P2(0,0,0,4h)

  P3(m,m√2,0,3h)

  P4(2m,0,0,2h)

とおくと,

  P0P1^2=3m^2+h^2*

  P0P2^2=3m^2+9h^2

  P0P3^2=4m^2+4h^2

  P0P4^2=3m^2+h^2*

  P1P2^2=16h^2

  P1P3^2=3m^2+9h^2

  P1P4^2=4m^2+4h^2

  P2P3^2=3m^2+h^2*

  P2P4^2=4m^2+4h^2

  P3P4^2=3m^2+h^2*

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

 4m^2+4h^2(3),16h^2(1)

H7は

  P3P4=P4P5=P5P6=P6P7=√7

  P3P5=P4P6=P5P7=√12

  P3P6=P4P7=√15

  P3P7=4

16h^2=16

3m^2+h^2=7

4m^2+4h^2=12

3m^2+9h^2=15

h^2=1,m^2=2は条件を満たす.

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