>>870
D = {(x,y)|x^2+y^2+z^2≦1}　→　D = {(x,y,z)|x^2+y^2+z^2≦1}
z=r･cosθ
y=r･sinθ･sinφ
x=r･sinθ･cosφ
と置換して、0≦r≦1,0≦θ≦π,0≦φ≦2π
∫∫∫dxdydz/√(1-x^2-y^2-z^2) =∫∫∫r^2･sinθ/√(1-r^2)　drdθdφ
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