41X1+412x2 Di> 21X1+a22X2 D- 上页 返回
+ = + = . , 2 1 1 2 2 2 2 1 1 1 1 2 2 1 a x a x b a x a x b , 21 22 11 12 a a a a D =
aan 021x1+a2x2 D a11+a122 a21X1+22x2 D= 0 上页 区回
+ = + = . , 2 1 1 2 2 2 2 1 1 1 1 2 2 1 a x a x b a x a x b , 2 22 1 12 1 b a b a D = + = + = . , 2 1 1 2 2 2 2 1 1 1 1 2 2 1 a x a x b a x a x b , 21 22 11 12 a a a a D =
因 b142 D1b2 a+2x2 21K1+422 D2= b 上页 返回
+ = + = . , 2 1 1 2 2 2 2 1 1 1 1 2 2 1 a x a x b a x a x b , 2 22 1 12 1 b a b a D = + = + = . , 2 1 1 2 2 2 2 1 1 1 1 2 2 1 a x a x b a x a x b . 21 2 11 1 2 a b a b D =
则二元线性方程组的解为 L12 D b2 422 X1= D. 21 D 411 12 x2= D 01 12 021 L22 21 L22 注意 分母都为原方程组的系数行列式 上页
则二元线性方程组的解为 , 2 1 2 2 1 1 1 2 2 2 2 1 1 2 1 1 a a a a b a b a D D x = = 注意 分母都为原方程组的系数行列式. . 2 1 2 2 1 1 1 2 2 1 2 1 1 1 2 2 a a a a a b a b D D x = =
例1求解二元线性方程组 J3x1-2x2=12, 2x1+x2=1. 解 =3-(-4)=7≠0， =-21 D2-21=-3 7 区回
例 1 + = − = 2 1. 3 2 12, 1 2 1 2 x x x x 求解二元线性方程组 解 2 1 3 − 2 D = = 3 − ( − 4 ) = 7 0 , 1 1 12 2 1 − D = = 14 , 2 1 3 12 D 2 = = −21 , DD x 1 1 = 2 , 7 14 = = DD x 2 2 = 3. 7 21 = − − =