■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
===================================
△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
===================================
△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
===================================
△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
===================================
[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.
===================================