■単純リー環を使った面数数え上げ(その158)

 億劫がらずに3次元5回回転対称図形を扱うことにした.

  a1=1,a2=√(1/3),a3=τ^2/√3

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[1]{3,5}(010)

  1−y1=(y2−y3)/√(3+3/τ^4)=0→y1=1(辺の二等分点),y2=y3=0

  (y1−y2)/√4=L,L=1/2

  c0=a1^2(1−y1)+a2^2(1−y2)+a3^2(1−y3)=1/3+τ^4/3

  d0=(1+1/3+τ^4/3)^1/2=(4/3+τ^4/3)^1/2

  h0=(1+τ^4)/3・√{3/(4+τ^4)}

  c2=a3^2(1−y3)=τ^4/3

  ‖d2‖=(a3^2)^1/2=τ^2/√3

  h2=|c2|/‖d2‖=τ^2/√3

 また,

→V2=1/2・tan54°×5/2={(5+2√5)/5}^1/2・5/4(正五角形の面積)

→Λ2=√3/4(正三角形の面積)

  3V・2L=(N0・V2・h0+N2・Λ2・h2)

={12・5{(5+2√5)/5}^1/2/4・(1+τ^4)/√{3(4+τ^4)}+20・√3/4・τ^2/√3}

=τ√5・(1+τ^4)+5τ^2

V=τ√5・(1+τ^4)/3+5τ^2/3

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[2]{3,5}(011)

  1−y1=0

  (y1−y2)/√4=(y2−y3)/√(3+3/τ^4)=L

  √(3+3/τ^4)=3/τ→y1=1,y2=3/(2τ+3)=3(4−√5)/11,y3=0,L=(3√5−1)/22

  c0=a1^2(1−y1)+a2^2(1−y2)+a3^2(1−y3)=(3√5−1)/33+τ^4/3

  d0=(1+1/3+τ^4/3)^1/2=(4/3+τ^4/3)^1/2

  h0=((3√5−1)/33+τ^4/3)・√{3/(4+τ^4)}

  c2=a3^2(1−y3)=τ^4/3

  ‖d2‖=(a3^2)^1/2=τ^2/√3

  h2=|c2|/‖d2‖=τ^2/√3

 また,

→V2=1/2・tan72°×10/2={(5+2√5)}^1/2・10/4(正十角形の面積)

→Λ2=√3/4(正三角形の面積)

  3V・2L=(N0・V2・h0+N2・Λ2・h2)

={12・10{(5+2√5)}^1/2/4・((3√5−1)/33+τ^4/3)・√{3/(4+τ^4)}+20・√3/4・τ^2/√3}

=30τ((3√5−1)/33+τ^4/3)+5τ^2

=10τ(3√5−1)/11+10τ^5+5τ^2

V={10τ(3√5−1)/11+10τ^5+5τ^2}/6L

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