转化到极坐标系,则x²+y²=r²,x=rcosθ,y=rsinθ积分域D={(x,y)|x²+y²≤R²}={(r,θ)|0≤r≤R,0≤θ≤2π}∫∫1/(x²+y²+R²)dxdy=∫∫ r/(r²+R²)drdθ=∫(0,2π...