■等面単体の体積(その305)
135→(√10,√10,√12)に注目して
P1(0,0,0,0)
P3(√3,√7,0,0)
P5(√12,0,0,0)
P2(x,y,z,0)とおくと
x^2+y^2+z^2=6
(x−√3)^2+(y−√7)^2+z^2=6
(x−√12)^2+y^2+z^2=12
(x−√12)^2+6−x^2=12
−2x√12+6=0→x=(√3)/2
y^2+z^2=6−3/4=21/4
3/4+(y−√7)^2+21/4−y^2=6
−2y√7+7=0→y=(√7)/2
z^2=21/4−7/4=14/4→z=(√14)/2
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P1(0,0,0,0)
P2((√3)/2,(√7)/2,(√14)/2,0)
P3(√3,√7,0,0)
P5(√12,0,0,0)
P4(x,y,z,w)とおく.
P1P2=P2P3=P3P4=P4P5=P5P6=√6
P1P3=P2P4=P3P5=P4P6=√10
P1P4=P2P5=P3P6=√12
P1P5=P2P6=√12
P1P6=√10
より
x^2+y^2+z^2+w^2=12
(x−√3/2)^2+(y−√7/2)^2+(z−√14/2)^2+w^2=10
(x−√3)^2+(y−√7)^2+z^2+w^2=6
(x−√12)^2+y^2+z^2+w^2=6
(x−√12)^2+12−x^2=6
−2x√12=−18→x=9/√12
y^2+z^2+w^2=12−81/12=63/12
9/12+(y−√7)^2+z^2+w^2=6
9/12+(y−√7)^2+63/12−y^2=6
−2y√7+13=6→y=(√7)/2
z^2+w^2=63/12−7/4=42/12
3+(z−√14/2)^2+w^2=10
3+(z−√14/2)^2+42/12−z^2=10
−z√14+14/4+3+14/4=10
−z√14+10=10→z=0,w=(√14)/2
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