简答题:设二维随机变量(X，y)的分布律为 <br /> <img src="http://www.weimei168.com/uploads/202208/161223741834201.png" width="185" height="106" /><br /> 求：(1)E(X)，E(Y)； <br /> (2)D(X)，D(Y)； <br /> (3)<img src="http://www.weimei168.com/uploads/202208/161223742341141.png" width="35" height="29" />．