13.(1)设θ是参数θ的无偏估计,且有 (hat (theta ))gt 0, 试证 (overrightarrow {theta )}^2=((overrightarrow {theta ))}^2 不是θ^2的-|||-无偏估计.-|||-(2)试证明均匀分布-|||-f(x)= { , 0lt xleqslant theta 0, .-|||-中未知参数θ的最大似然估计量不是无偏的.