a11*+a122=bu 211+a22x2 D 11a 12 2 上
+ = + = . , 21 1 22 2 2 11 1 12 2 1 a x a x b a x a x b , 21 22 11 12 a a a a D =
a21x1+a2x2=b2 D I1 21X1+a2 D
+ = + = . , 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 22 11 12 a a a a D =
11+a12x a21x1+a2x2=b2 D1 12 = 22 I1 11 +12x2 211+a 22 D,=ll 21 上
+ = + = . , 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 =
则二元线性方程组的解为 b a12 a. b D, b 22 D x,=-2= 21 D11 a12 D a11 12 21 22 21 22 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 , 21 22 11 12 2 22 1 12 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. . 21 22 11 12 21 2 11 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 3x1-2x2=12 2x1+x2=1 解 3-2 D=2 =3-(-4)=7≠0, 11=14,D,=3 D、12 2 2 =-21, 21 D114 D =2,12=s-21 3. D7 D 7 上页
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 = − − =