, 3 D,0 X,= D67 =0, D673 67 D D,67 X= 1 D672 D67 例3问取何值时,齐次方程组 (1-x)x1-2x2+4x3=0, 2x1+(3-)x2+x3=0, x1+x2+(-A)x3=0, 有非零解? 上或, D D x 3 1 67 3 67 1  1 = = = , D D x 0 67 0 2 2 = = = , D D x 2 1 67 2 67 3 3 = = = 1. 67 4 67 4 = = = D D x 例3 问 取何值时，齐次方程组 ( ) ( ) ( )      + + − = + − + = − − + = 1 0, 2 3 0, 1 2 4 0, 1 2 3 1 2 3 1 2 3 x x x x x x x x x    有非零解？ 