概车纶与款理统外 pZ☑=D+Dr2+2Cm(32 ())Cw(x.Y) D(X)+D)D(DY) =1+4-2=3.) 2 , 3 ) 2Cov( 2 ) ( 3 ( ) ( Y X Y D X D Z = D + + Cov( , ) 3 1 ( ) 4 1 ( ) 9 1 = D X + D Y + X Y ( ) ( ) 3 1 ( ) 4 1 ( ) 9 1 = D X + D Y + ρXY D X D Y = 1+ 4 − 2 = 3