■等面単体の体積(その285)
P1(0,0,0,0,0)
P2(√2,√3,0,0,0)
P3(√8,0,0,0,0)
P4(√(9/2),0,√(9/2),0,0)
P5(√2,0,√2,2,0)
は
P1P2=P2P3=P3P4=P4P5=√5
P1P3=P2P4=P3P5=√8
P1P4=P2P5=3
P1P5=√8
を満たす.
P0(a,b,c,d,e)とおいて,
P0P1=P1P2=P2P3=P3P4=P4P5=√5
P0P2=P1P3=P2P4=P3P5=√8
P0P3=P1P4=P2P5=3
P0P4=P1P5=√8
P0P5=√5
を満たすように配置する.
a^2+b^2+c^2+d^2+e^2=5
(a−√2)^2+(b−√3)^2+c^2+d^2+e^2=8
(a−√8)^2+b^2+c^2+d^2+e^2=9
(a−√(9/2))^2+b^2+(c−√(9/2))^2+d^2+e^2=8
(a−√2)^2+b^2+(c−√2))^2+(d−2)^2+e^2=5
(a−√8)^2+5−a^2=9
−2a√8=−4→a=√(1/2)
1/2+b^2+c^2+d^2+e^2=5
1/2+(b−√3)^2+c^2+d^2+e^2=8
(b−√3)^2+5−b^2=8→b=0
1/2+c^2+d^2+e^2=5
2+(c−√(9/2))^2+d^2+e^2=8
2+(c−√(9/2))^2+5−c^2−1/2=8
2c√(9/2)=3→c=√(1/2)
d^2+e^2=4
1/2+1/2+(d−2)^2+e^2=5
1/2+1/2+(d−2)^2+4−d^2=5→d=1,e=√3
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