极坐标下D:x^2+y^2≤1,x≥0,y≥0可表示为0≤r≤1,0≤θ≤π/2∫∫√(1-x^2-y^2)/(1+x^2+y^2)dxdy=∫(0,π/2)dθ∫(0,1)[(1-r^2)/(1+r^2)]rdr=π/2∫(0,1)[(1-r^2)/(1+r^2)]rdr,=π/2∫(0,1)r/(1+r^2)dr-(π/2)∫(0,1...只有D求对了 后面就太离谱了如图：