∫∫(x^2+ y^2)^(-2)dxdy D是(x-1)^2+ y^2=1内且x≥1的部分
=2∫[0,π/4]dθ∫[1/cosθ,2cosθ](ρ^2)^(-2)ρdρ
=2∫[0,π/4]dθ∫[1/cosθ,2cosθ]ρ^(-3)dρ
=-∫[0,π/4]ρ^(-2)|[1/cosθ,2cosθ]dθ
=∫[0,π/4][(cosθ)^2)-1/4(cosθ)^(-2)]dθ
=1/2∫[0,π/4](1+cos2θ)dθ-1/4tanθ|[0,π/4]
=1/2*π/4+1/4sin2θ|[0,π/4]-1/4
=π/8+1/4-1/4
=π/8