>298
x = 1/2 + r･cosθ, y=r･sinθ　(0≦r≦1/2, 0≦θ<2π) とおく。
x^2 + y^2 = 1/4 + r･cosθ + r^2.
∬_D (x^2+y^2)dxdy = ∫_[0,1/2] ∫_[0,2π] (1/4 + r･cosθ + r^2)dθ rdr
　= 2π{(1/8)r^2 + (1/4)r^4 ](r=0→1/2) = 3π/32.