X1=22-D2412 bau -has a11a22-a12a21 a1 11<22 1221 定义二阶行列式为 a11a12 a11a22-a12a a21a22 用行列式的记号,方程组的解可表为 b1a12 a11 b1 h2 a a21 b 2 X1= a11a12 X2 a11a12 a21a22 a21a22 上页1 22 2 12 2 11 1 21 1 2 11 22 12 21 11 22 12 21 , . b a b a b a b a x x a a a a a a a a − − = = − − 定义二阶行列式为 1 1 1 2 1 1 2 2 1 2 2 1 2 1 2 2 . a a a a a a a a = − 用行列式的记号,方程组的解可表为 1 12 11 1 2 22 21 2 1 2 11 12 11 12 21 22 21 22 , . b a a b b a a b x x a a a a a a a a = =