+3x1=-1 2x1-x2+2x3+4x4 3x1-x2+4x3+4x4=-3 5x,-3x+x2+20x,=-2 将第1个方程乘(2)(-3),(-5)分别加到234个 方程上,得 +3x,=-1 4 x+2x,-2x1=0 2xn+4x2-5x,=0 2x+x,+5x=3 5 2021/2/202021/2/20 5 将第1个方程乘(−2),(−3),(−5)分别加到2,3,4个 方程上, 得 1 2 4 2 3 4 2 3 4 2 3 4 3 1 2 2 0 2 4 5 0 2 5 3 x x x x x x x x x x x x  − + = −   + − =  + − =    + + = 1 2 4 1 2 3 4 1 2 3 4 1 2 3 4 3 1 2 2 4 2 3 4 4 3 5 3 20 2 x x x x x x x x x x x x x x x  − + = −   − + + = −  − + + = −    − + + = −