中,最有效的估计量是:a:2/3*x1+1/3*x2; b:1/4*x1+3/4*x2; c:1/2*x1+1/2*x2
怎么算出来的?
D(1/2*x1+1/2*x2)=1/2*D(X) D(2/3*x1+1/3*x2)=5/9*D(X)D(1/4*x1+3/4*x2)=10/16*D(X)1/2 < 5/9 < 10/16如果正确,请采纳,谢谢