■サマーヴィルの等面四面体(その563)
【1】F5 in F4
△5を
P0(m/2,m√5/2,0,m√10/2,h)
P1(0,0,0,0,0)
P2(0,0,0,0,5h)
P3(2m,0,0,0,4h)
P4(3m/2,m√5/2,m√10/2,0,3h)
P5(m,m√5,0,0,2h)
としてみる.
P0P1^2=4m^2+h^2
P0P2^2=4m^2+16h^2
P0P3^2=6m^2+9h^2
P0P4^2=6m^2+4h^2
P0P5^2=4m^2+h^2
P1P2^2=25h^2
P1P3^2=4m^2+16h^2
P1P4^2=6m^2+9h^2
P1P5^2=6m^2+4h^2
P2P3^2=4m^2+h^2
P2P4^2=6m^2+4h^2
P2P5^2=6m^2+9h^2
P3P4^2=4m^2+h^2
P3P5^2=6m^2+4h^2
P4P5^2=4m^2+h^2
4m^2+h^2(5)<4m^2+16h^2(2)
6m^2+4h^2(4)<6m^2+9h^2(3)
25h^2(1)
25h^2=4m^2+h^2=5,h^2=1/5,m^2=6h^2=6/5
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P0を外すと,等間隔ではなくなる点に注意して
P1P2^2=25h^2
P1P3^2=4m^2+16h^2
P1P4^2=6m^2+9h^2
P1P5^2=6m^2+4h^2
P2P3^2=4m^2+h^2
P2P4^2=6m^2+4h^2
P2P5^2=6m^2+9h^2
P3P4^2=4m^2+h^2
P3P5^2=6m^2+4h^2
P4P5^2=4m^2+h^2
25h^2(1)=4m^2+h^2(3)<4m^2+16h^2(1)
6m^2+4h^2(3)<6m^2+9h^2(2)
F5は
P1P2=P2P3=P3P4=P4P5=√5
P1P3=P2P4=P3P5=√8
P1P4=P2P5=3
P1P5=√8
であるから,
25h^2=4m^2+h^2=5,6m^2+4h^2=8
6m^2+9h^2=9,4m^2+16h^2=8,m^2=6h^2
h^2=1/5,m^2=6/5
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また,
P1(0,0,0,0,0)
P2(0,0,0,0,5h)
P3(2m,0,0,0,4h)
P4(3m/2,m√5/2,m√10/2,0,3h)
P5(m,m√5,0,0,2h)
のQ(x,y,z,w)がF4を形成すればよいのであるが,
P2P3^2=4m^2
P2P4^2=6m^2
P2P5^2=4m^2
P3P4^2=4m^2
P3P5^2=6m^2
P4P5^2=4m^2
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【2】G5 in G4
次に外すとなったら,P5だろうか? この場合も等間隔ではなくなる点に注意して
P1P2^2=25h^2
P1P3^2=4m^2+16h^2
P1P4^2=6m^2+9h^2
P2P3^2=4m^2+h^2
P2P4^2=6m^2+4h^2
P3P4^2=4m^2+h^2
25h^2(1)=4m^2+h^2(2)<4m^2+16h^2(1)
=6m^2+4h^2(1)<6m^2+9h^2(1)
G5は
P2P3=P3P4=P4P5=√5
P2P4=P3P5=√8
P2P5=3
であるから,
25h^2=4m^2+h^2=5,4m^2+16h^2=6m^2+4h^2=8
6m^2+9h^2=9
h^2=1/5,m^2=6/5はこれを満たす.
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また,
P1(0,0,0,0,0)
P2(0,0,0,0,5h)
P3(2m,0,0,0,4h)
P4(3m/2,m√5/2,m√10/2,0,3h)
Q(x,y,z,w)がG4を形成すればよいのであるが,
P2P4^2=4m^2
P2P4^2=4m^2
P3P4^2=6m^2
これが(4,6,6)であれば問題が残ったが(4,4,6)なので(OK).
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