■五芒星と掛谷の問題(その39)

(その32)をやり直し

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(rcosθ、rsinθ)と(rcos(π-2θ),rsin(π-2θ))=(-rcos2θ,rsin2θ)を結ぶ直線

y=(rsin2θ-rsinθ/(-rcos2θ-rcosθ)・(x-rcosθ)+rsinθ

(rcosθ、-rsinθ)と(1,0)を結ぶ直線

y=(rsinθ)/(1-rcosθ)(x-rcosθ)-rsinθ

の交点を求める

(rsin2θ-rsinθ)/(-rcos2θ-rcosθ)・(x-rcosθ)-(rsinθ)/(1-rcosθ)・(x-rcosθ)=-2rsinθ

{(rsin2θ-rsinθ)(1-rcosθ)-(rsinθ)(-rcos2θ-rcosθ)}・(x-rcosθ)=-2rsinθ(-rcos2θ-rcosθ)(1-rcosθ)

ここで、n=3の場合も計算できることになる。

{(2cosθ-1)(1-rcosθ)+r(cos2θ+cosθ)}・(x-rcosθ)=2r(cos2θ+cosθ)(1-rcosθ)

{2cosθ-1-2r(cosθ)^2+rcosθ+2r(cosθ)^2-r+rcosθ)}・(x-rcosθ)=2r(cos2θ+cosθ)(1-rcosθ)

{2cosθ-1+2rcosθ-r}・(x-rcosθ)=2r(cos2θ+cosθ)(1-rcosθ)

{2cosθ(1+r)-(1+r)}・(x-rcosθ)=2r(cos2θ+cosθ)(1-rcosθ)

(2cosθ-1)(1+r)・(x-rcosθ)=2r(cosθ+1)(2cosθ-1)(1-rcosθ)

(1+r)・(x-rcosθ)=2r(cosθ+1)(1-rcosθ)

x-rcosθ=2r(cosθ+1)(1-rcosθ)/(1+r)

y+rsinθ=(rsinθ)/(1-rcosθ)・(x-rcosθ)=2r(cosθ+1)(rsinθ)/(1+r)

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(rcosθ、rsinθ)と(rcos(π-2θ),rsin(π-2θ))=(-rcos2θ,rsin2θ)の中点((rcosθ-rcos2θ)/2,((rsinθ+rsin2θ)/2)

からの距離の2乗は

L^2={2r(cosθ+1)(1-rcosθ)/(1+r)+rcosθ-(rcosθ-rcos2θ)/2}^2+{2r(cosθ+1)(rsinθ)/(1+r)-rsinθ-((rsinθ+rsin2θ)/2}^2

{2r(cosθ+1)(1-rcosθ)/(1+r)+r(cosθ+cos2θ)/2}^2+{2r(cosθ+1)(rsinθ)/(1+r)-r(3sinθ+sin2θ)/2}^2

{2r(cosθ+1)(1-rcosθ)/(1+r)+r(cosθ+1)(2cosθ-1))/2}^2+{2r(cosθ+1)(rsinθ)/(1+r)-rsinθ(3+2cosθ)/2}^2

={r(cosθ+1)}^2{4(1-rcosθ)/2(1+r)+(1+r)(2cosθ-1))/2(1+r)}^2+(rsinθ)^2{2r(cosθ+1)/(1+r)-(3+2cosθ)/2}^2

={r(cosθ+1)}^2{(2cosθ(1-r)+3-r)/2(1+r)}^2+(rsinθ)^2{(2cosθ(1-r)+3-r)/2(1+r)}^2

=r^2(2cosθ+2){(2cosθ(1-r)+3-r)/2(1+r)}^2

=r^2(2cos(θ/2))^2{(2cosθ(1-r)+3-r)/2(1+r)}^2

=(rcos(θ/2))^2{(2cosθ(1-r)+3-r)/(1+r)}^2

=(rcos(θ/2))^2{(2cosθ(1-r)+3-r)/(1+r)}^2

(rcos(θ/2))^2{(2cos(θ/2))^2(1-r)+(1+r))/(1+r)}^2

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2Lと1+rの比較が問題となる これにより結論自体を大きく変更せざるを得なくなった。

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r=1/6

n=3: 0.318123→0.526056

n=5: 0.359868→0.379365

n=7: 0.3719

n=9: 0.37692

n=11: 0.379476

n=13: 0.380951

n=21: 0.383251

n=41: 0.384308

n=61: 0.384515

n=81: 0.384588

n=101: 0.384623

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r=1/10

n=3: 0.214719→0.725685

n=5: 0.242886→0.51794

n=7: 0.251007→0.472759

n=9: 0.254395→0.455425

n=11: 0.25612→0.446916

n=13: 0.257116→0.4421

n=21: 0.258668→0.434724

n=41: 0.259382→0.431388

n=61: 0.259521→0.430741

n=81: 0.25957→0.430511

n=101: 0.259594→0.430403

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r=1/108

n=3: 0.0236169→6.00993

n=5: 0.0267152→4.2345

n=7: 0.0276084→3.85272

n=9: 0.0279811→3.70671

n=11: 0.0281709→3.63513

n=13: 0.0282804→3.59464

n=21: 0.0284511→3.53269

n=41: 0.0285296→3.50466

n=61: 0.0285449→3.49923

n=81: 0.0285504→3.4973

n=101: 0.0285529→3.49639

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