a1x1+a12x2=b1, 21X1+a1 21 2 =b 12 D1= 22 aux+aurra=b,, 211+ 22 b2 11 b 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 =