((X)_(1)+(X)_(2)+(X)_(3))/3 b.X1-|||-c. ((X)_(1)+(X)_(2))/2 d. (2(X)_(1)+(X)_(2)+(X)_(3))/4-|||-则无偏估计是 __ ,其中最有效的是 __

(x)_(1)+2(x)_(2)+2(x)_(3)geqslant 4-|||-(x)_(1)+4(x)_(2)leqslant 20-|||-(x)_(1)+

设x 1 2 4-|||-f(x)= 2 2 1 2-x-|||-1 2 一 x 2 4-|||-1 x x+3 x+6，证明：x 1 2 4-|||-f(x)

dfrac (1)(x) C. -dfrac (1)({x)^2} D. dfrac (2)({x)^3}

) (x)_(1)+4(x)_(2)-2(x)_(3)+8(x)_(4)=2 -(x)_(1)+2(x)_(2)+3(x)_(3)+4(x)_(4)=1 (x)

1.已知方程组 ) (x)_(1)+(x)_(2)+(x)_(3)+(x)_(4)=2 3(x)_(1)+2(x)_(2)+(x)_(3)+(x)_(4)=a

线性方程组 ) (x)_(1)+2(x)_(2)-2(x)_(3)=1 2(x)_(1)+4(x)_(2)-4(x)_(3)=2 3(x)_(1)+6(x)_

解方程_(2)-3(x)_(3)+4(x)_(4)=-5-|||-x1- 2x3+324 =-4-|||-(x)_(1)+2(x)_(2)-5(x)_(4)=1

2.解方程组 ) (x)_(1)+(x)_(2)+(x)_(3) (x)_(1)+(x)_(2)-(x)_(3)-(x)_(4)=1 5(x)_(1)+5(

求二次型 ((x)_(1),(x)_(2),(x)_(3))=4({x)_(2)}^2-3({x)_(3)}^2+4(x)_(1)(x)_(2)-4(x)_(1

用消元法解下列线性方程组:-|||- x1+3x2+5x3-4x4 =1, x1+3x2+2x3-2x4+x5=-1, x1-2x2+x3-x4-x5=3, x