■フルヴィッツ曲線(その127)

x=(n-2)acos(nθ)+nacos(n-2)θ-2Rsinθ

y=-(n-2)asin(nθ)+nasin(n-2)θ-2Rcosθ

  xsinθ−ycosθ=p(θ)

に代入すると

(n-2)asin(n+1)θ-nasin(n-3)θ+2Rcos2θ=p(θ)

内転形条件について確認しておきたい。

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[1]n=3のとき

p(θ)=asin4θ+2Rcos2θ

ω=2π/3として

p(θ+ω)=asin(4θ+4ω)+2Rcos(2θ+2ω)

p(θ-ω)=asin(4θ-4ω)+2Rcos(2θ-2ω)

p(θ+ω)+p(θ-ω)=2asin(4θ)cos(4ω)+4Rcos(2θ)cos(2ω)

=-asin(4θ)-2Rcos(2θ)

p(θ)+p(θ+ω)+p(θ-ω)=0

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[2]n=4のとき

p(θ)=2asin5θ-4asinθ+2Rcos2θ

ω=π/2として

p(θ+ω)=2asin(5θ+5ω)-4asin(θ+ω)+2Rcos(2θ+2ω)

p(θ-ω)=2asin(5θ-5ω)-4asin(θ-ω)+2Rcos(2θ-2ω)

p(θ+ω)+p(θ-ω)=4asin(5θ)cos(5ω)-8asin(θ)cos(ω)+4Rcos(2θ)cos(2ω)=-4Rcos(2θ)

p(θ+2ω)=2asin(5θ+10ω)-4asin(θ+2ω)+2Rcos(2θ+4ω)

=-2asin(5θ)+4asin(θ)+2Rcos(2θ)

p(θ)+p(θ+2ω)=4Rcos(2θ)

p(θ)+p(θ+ω)+p(θ-ω)+p(θ+2ω)=0

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