■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)

  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

===================================