带根号函数求积分请问这个的积分如何求?

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带根号函数求积分请问这个的积分如何求?
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带根号函数求积分请问这个的积分如何求?
带根号函数求积分

请问这个的积分如何求?

带根号函数求积分请问这个的积分如何求?
∵∫√(1-r^2)rdr
=(1/2)∫√(1-r^2)d(r^2)=-(1/2)∫√(1-r^2)d(1-r^2)
=-(1/2)×(2/3)(1-r^2)^(3/2)+C=-(1/3)(1-r^2)^(3/2)+C,
∴∫(上限为sinθ,下限为0)√(1-r^2)rdr
=-(1/3)(1-r^2)^(3/2)|(上限为sinθ,下限为0)
=-(1/3)[1-(sinθ)^2]^(3/2)+(1/3)[1-0^2]^(3/2)
=(1/3)[1-(cosθ)^3],
∴∫(上限为π/2,0)dθ∫(上限为sinθ,下限为0)√(1-r^2)rdr
=(1/3)∫(上限为π/2,0)[1-(cosθ)^3]dθ,
∵∫[1-(cosθ)^3]dθ
=∫dθ-∫(cosθ)^3]dθ=θ-∫(cosθ)^2d(sinθ)=θ-∫[1-(sinθ)^2]d(sinθ)
=θ-∫d(sinθ)+∫(sinθ)^2d(sinθ)=θ-sinθ+(1/3)(sinθ)^3+C,
∴∫(上限为π/2,0)dθ∫(上限为sinθ,下限为0)√(1-r^2)rdr
=(1/3)∫(上限为π/2,0)[1-(cosθ)^3]dθ
=(1/3)[θ-sinθ+(1/3)(sinθ)^3]|(上限为π/2,0)
=(1/3){π/2-sin(π/2)+(1/3)[sin(π/2)]^3}
 -(1/3){0-sin0+(1/3)[sin0]^3}
=(1/3)(π/2-1+1/3)
=π/6-2/9.

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