■葉序らせん(その74)

 OA=OC=ODより,

Y^2+b^2s^2=(Y−h)^2=(Y−y)^2+x^2c^2

Y^2+b^2s^2=Y^2−2yY+y^2+x^2c^2=Y^2−2hY+h^2

2yY=y^2+x^2c^2−b^2s^2

2hY=h^2−b^2s^2

h(y^2+x^2c^2−b^2s^2)=y(h^2−b^2s^2)

h(y^2+x^2−x^2s^2−b^2s^2)=y(h^2−b^2s^2)

(−hx^2−hb^2+yb^2)s^2=yh^2−h(x^2+y^2)

h^2+b^2=1

x^2+y^2=h^2

b^2=−2hy+h^2

y=(h^2−b^2)/2h=(2h^2−1)/2h

y^2=(2h^2−1)^2/4h^2

x^2=h^2−y^2

−b^2=x^2+y^2−1

を代入すると

y−h=−1/2h

(−hx^2+(y−h)b^2)s^2=yh^2−h(x^2+y^2)=h^2(y−h)

(−hx^2−b^2/2h)s^2=−h/2

s^2=−1/2(−x^2−b^2/2h^2)

y/h−1=−1/2h^2より

s^2=−1/2{(y/h−1)b^2−x^2}

Y=(h^2−b^2s^2)/2h

これより,s^2,c^2,Yは求められる.

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

  A(−bs,−Y,bc)

  B(bs,−Y,bc)

  C(0,h−Y,0)

  D(cx,y−Y,sx)

  E(−cx,y−Y,−sx)

  F(αc−γs,β−Y,αs+γc)

  G(ξc−ζs,η−Y,ξs+ζc)

  O(0,0,0)として,

cos(∠AOC)=cos(∠AOD)を求めればよい.

cos(∠AOC)=−Y(h−Y)/(b^2s^2+Y^2)^1/2・(h−Y)

=−Y/(b^2s^2+Y^2)^1/2

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