■ピザの分割(その10)

  y=zcos(θ−α)

  dy/dθ=−zsin(θ−α)

とおく.

  z^2−y^2=(zsin(θ−α))^2

  r^2=2y^2+1−z^2−2y{y^2+1−z^2}^1/2

=y^2+1−(zsin(θ−α))^2−2y{1−(zsin(θ−α))^2}^1/2

  r^2dθ=y^2+1−(zsin(θ−α))^2−2y{1−(zsin(θ−α))^2}^1/2・dy/zsin(θ−α)

=(y^2+1)/zsin(θ−α)−zsin(θ−α)−2y{1/(zsin(θ−α))^2−1}^1/2・dy

 簡単な形にはならない.

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