3.设θ是参数θ的无偏估计,且有 (hat (theta ))gt 0, 试证 (theta )^2=((theta ))^2 不是θ^2的无偏估计.-|||-4.设X1,X2,···,Nn是来自参数为λ的泊松分布的简单随机样本,试求λ^2的无偏估计量.-|||-5.设X1,X2,···,Nn来自参数为n,p的二项分布总体,试求p ^2的无偏估计量.-|||-_(1)=dfrac (2)(3)(X)_(1)+dfrac (1)(3)(X)_(2) , (hat {m)}_(2)=dfrac (1)(4)(X)_(1)+dfrac (3)(4)(X)_(2) , _(3)=dfrac (1)(2)(X)_(1)+dfrac (1)(2)(X)_(2)-|||-都是m的无偏估计量;并问哪一个估计量的方差最小?