■サマーヴィルの等面四面体(その135)
135→(√12,√12,4)に注目して
P1(0,0,0,0)
P3(2,2√2,0,0)
P5(4,0,0,0)
P2(x,y,z,0)とおくと
x^2+y^2+z^2=7
(x−2)^2+(y−2√2)^2+z^2=7
(x−4)^2+y^2+z^2=15
(x−4)^2+7−x^2=15
−8x+16=8→x=1
y^2+z^2=6
1+(y−2√2)^2+6−y^2=7
−4√2y+8=0
y=√2,z=2
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P1(0,0,0,0)
P2(1,√2,2,0)
P3(2,2√2,0,0)
P5(4,0,0,0)
P4(x,y,z,w)とおく.
P0P1=P1P2=P2P3=P3P4=P4P5=P5P6=P6P7=√7
P0P2=P1P3=P2P4=P3P5=P4P6=P5P7=√12
P0P3=P1P4=P2P5=P3P6=P4P7=√15
P0P4=P1P5=P2P6=P3P7=4
P0P5=P1P6=P2P7=√15
P0P6=P1P7=√12
P0P7=√7
より
x^2+y^2+z^2+w^2=15
(x−1)^2+(y−√2)^2+(z−2)^2+w^2=12
(x−2)^2+(y−2√2)^2+z^2+w^2=7
(x−4)^2+y^2+z^2+w^2=7
(x−4)^2+15−x^2=7
−8x+31=7→x=3
y^2+z^2+w^2=6
4+(y−√2)^2+(z−2)^2+w^2=12
1+(y−2√2)^2+z^2+w^2=7
1+(y−2√2)^2+6−y^2=7
−4√2y+8+7=7→y=√2
z^2+w^2=4
(z−2)^2+w^2=8
(z−2)^2+4−z^2=8
−2z=0→z=0,w=2
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