aux+a12x2b a,ix, +anx,=b 12 22 X, ta 11~1 122 a21x1+a2x2=b2 b 11 21       . , 21 1 22 2 2 11 1 12 2 1 a x a x b a x a x b , 2 22 1 12 1 b a b a D         . , 21 1 22 2 2 11 1 12 2 1 a x a x b a x a x b . 21 2 11 1 2 a b a b D 