■等面単体の体積(その382)

  P1(0,0,0)

  P2(1/√2,√3/√2,0)

  P3(2/√2,0,0)

  P1P2=P2P3=√2

  P1P3=√2

を満たす.

  P1(0,0,0)

  P2(m/√2,m√3/√2,0)

  P3(2m/√2,0,0)

  P1P2=P2P3=m√2

  P1P3=m√2

を満たす.

  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+h^2

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

これでは,対辺にならないのでNG.

  P0(0,0,0)

  P1(0,0,3h)

  P2(m/√2,m√3/√2,h)

  P3(2m/√2,0,2h)

  P0P1^2=9h^2

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

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

  P1P2^2=2m^2+4h^2

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

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

ここで,

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

ならばよい.

  P0P1^2=9h^2

  P0P2^2=9h^2

  P0P3^2=12h^2

  P1P2^2=12h^2

  P1P3^2=9h^2

  P2P3^2=9h^2

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