D(xy)=E(x²y²)-E²(xy)=E(x²)E(y²)-E²(x)E²(y)D(x)=E(x²)-E²(x)D(y)=E(y²)-E²(y)E²(x)>=0E(x²)>姿猛=0所以D(x)D(y)=E(x²)E(y²)-E²(x)E²早蚂(y)-E²(x)E(y²迹睁桥)-E(x²)E²(y)=D(xy)-E²(x)E(y²)-E(x²)E²(y)<=D(xy)如有意见,欢迎讨论,共同学习;如有帮助,请选为满意回答!