(後只人季 x1+a12x,=b1, 11~1 21X1+2,X 21 2 11 a1x1+a12x2=b1, 211+a2x2=b2 21   + = + = . , 21 1 22 2 2 11 1 12 2 1 a x a x b a x a x b , 2 1 2 2 1 1 1 2 a a a a A =    + = + = . , 21 1 22 2 2 11 1 12 2 1 a x a x b a x a x b . 2 1 2 1 1 1 2 a b a b A =