>>439
>(x, y)=((θ+sinθcosθ)√(y0^3/2k), y0cos^2θ) (θ:0→π/2)
θ←θ/2
(x, y)=((θ+sinθ)√(y0^3/8k), (y0/2)(1+cosθ) (θ:0→π)
x=(arccos(2y/y0-1)+2√((y/y0)(1-y/y0)))√(y0^3/8k) (y:y0→0)
y=0 for x=π√(y0^3/8k)