(1)设随机变量X1,X2,X3相互独立,且有 _(1)sim b(4,dfrac (1)(2)) _(2)sim -|||-(6,dfrac (1)(3)), _(3)sim b(6,dfrac (1)(3)) 求 {X)_(1)=2,(X)_(2)=2,(X)_(3)=5} E(X1X2X3 ), ((X)_(1)--|||-_(2)), ((X)_(1)-2(X)_(2)).-|||-(2)设X,Y是随机变量,且有 E(X)=3 (X)=1, D(X)=4 (Y)=9,-|||-令 =5X-Y+15, 分别在下列3种情况下求E(Z)和D(Z).-|||-(i)X,Y相互独立,((ii)X,Y不相关,(iii) X与Y的相关系数为0.25.