二重积分∫∫(x^2+y^2)dxdy=∫（π/4,π/2）dθ∫（0,sinθ）r³dr
=1/4∫（π/4,π/2）(sinθ)^4dθ
=1/32∫（π/4,π/2）(3-4cos2θ+cos4θ)dθ
=1/32(3θ-2sin2θ+1/4sin4θ)|（π/4,π/2）
=1/32(3π/2-3π/4+2)
=（3π+8）/128.