易证:对于线性方程组 aux+a12x2+a3x3=6 c21x1+c22x2+a23x3 (2.2) a31x1+a2X2+a3x3=b3 13 当 D=la 22 23≠0 31 33易证： 对于线性方程组 31 1 32 2 33 3 3 21 1 22 2 23 3 2 11 1 12 2 13 3 1 a x a x a x b a x a x a x b a x a x a x b + + = + + = + + = (2.2) 当 31 32 33 21 22 23 11 12 13 a a a a a a a a a D =  0时