1.用消元法解二元线性方程组 +a12 12 1a2x1+a2x2=b2.(2) (1)×a2:a1p2x1+a12x2=b1a2 (2)xa12:a2421x1+a12a2x2=h2a12, 两式相减消去x2,得 1 11．用消元法解二元线性方程组    + = + = . , 21 1 22 2 2 11 1 12 2 1 a x a x b a x a x b (1) : a22 , a11a22 x1 + a12a22 x2 = b1a22 (2) : a12 , a12a21x1 + a12a22 x2 = b2a12 两式相减消去 x2，得 (1) (2) ; （a11a22 − a12a21）x1 = b1a22 − a12b2