y=a+bx+u,G X,+u y,=a+b y xu+u x lI B u XB+U( ) ( ) ( ) ( ) Y XB U U b a Y X B a b n a b a b a b i n u u u x x x y y y y x u y x u y x u y x u n n n n n n i i i = +               =         =               =               = = + + = + + = + + = + + =          2 1 2 1 2 1 2 2 2 1 1 1 1 1 1 2 1 1，2，