■等面単体の体積(その339)

 n=6の本体でわかっているのは2種類ある.

P0(2/√3,0,0,0,√(7/6),√(7/3))

P1(0,0,0,0,0,0)

P2((√3)/2,(√7)/2,(√14)/2,0,0,0)

P3(√3,√7,0,0,0,0)

P4(9/√12,(√7)/2,0,(√14)/2,0,0)

P5(√12,0,0,0,0,0)

P6(4/√3,0,0,0,√(14/3),0)

  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

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 P0との距離が最短なのはP1かP6であるが,ここではP1を外してみる.

P1=P2+sP0P1=((√3)/2,(√7)/2,(√14)/2,0,0,0)+s(2/√3,0,0,0,√(7/6),√(7/2))

 ベクトルs(2/√3,0,0,0,√(7/6),√(7/2))と直交するP1を通る平面

  √8a+√7e+√21f=0

との交点を求める.

Q0=Q1(0,0,0,0,0,0)

Q2は,b=√7/2,c=√14/2,d=0

  (a−√3/2)/√8=e/√7=f/√21=k

  a=√3/2+√8k,e=√7k,f=√21k

  √8a+√7e+√21f=0に代入

  √6+8k+7k+21k=0,k=−√6/36

Q2(14√3/36,√7/2,√14/2,0,−√42/36,−√126/36)

Q3は,b=√7,c=0,d=0

  (a−√3)/√8=e/√7=f/√21=k

  a=√3+√8k,e=√7k,f=√21k

  √8a+√7e+√21f=0に代入

  2√6+8k+7k+21=0,k=−√6/18

Q3(14√3/18,√7,0,0,−√42/18,−√126/18)

Q4は,b=√7/2,c=0,d=√14/2

  (a−9/√12)/√8=e/√7=f/√21=k

  a=9/√12+√8k,e=√7k,f=√21k

  √8a+√7e+√21f=0に代入

  3√6+8k+7k+21=0,k=−√6/12

Q4(7√3/6,√7/2,0,√14/2,−√42/12,−√126/12)

Q5は,b=0,c=0,d=0

  (a−√12)/√8=e/√7=f/√21=k

  a=√12+√8k,e=√7k,f=√21k

  √8a+√7e+√21f=0に代入

  4√6+8k+7k+21=0,k=−√6/9

Q5(14√3/9,0,0,0,−√42/9,−√126/9)

Q6は,b=0,c=0,d=0

 (a−4/√3)/√8=(e−√(14/3))/√7=f/√21=k

  a=4/√3+√8k,e=√(14/3)+√7k,f=√21k

  √8a+√7e+√21f=0に代入

  8√6/3+8k+7√6/3+7k+21k=0,k=−5√6/36

Q6(28√3/36,0,0,0,7√42/36,−5√126/36)

Q1(0,0,0,0,0,0)

Q2(14√3/36,18√7/36,18√14/36,0,−√42/36,−√126/36)

Q3(28√3/36,36√7/36,0,0,−2√42/36,−2√126/36)

Q4(42√3/36,18√7/36,0,18√14/36,−3√42/36,−3√126/36)

Q5(56√3/36,0,0,0,−4√42/36,−4√126/36)

Q6(28√3/36,0,0,0,7√42/36,−5√126/36)

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Q1Q2^2=7560/36^2

Q1Q3^2=12096/36^2

Q1Q4^2=13608/36^2

Q1Q5^2=12096/36^2

Q1Q6^2=7560/36^2

Q2Q3^2=7560/36^2

Q2Q4^2=7560/36^2

Q2Q5^2=13608/36^2

Q2Q6^2=12096/36^2

Q3Q4^2=7560/36^2

Q3Q5^2=12096/36^2

Q3Q6^2=13608/36^2

Q4Q5^2=7560/36^2

Q4Q6^2=12096/36^2

Q5Q6^2=7560/36^2

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[まとめ]n=5のときの本体になっている.

  P0P1=P1P2=P2P3=P3P4=P4P5=√5

  P0P2=P1P3=P2P4=P3P5=√8

  P0P3=P1P4=P2P5=3

  P0P4=P1P5=√8

  P0P5=√5

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