（急）!利用矩阵的初等变换求解下列线性方程组,要有完整的过程.
（急）!利用矩阵的初等变换求解下列线性方程组,要有完整的过程.x1+5x2-x3-x4=-1
x1-2x2+x3+3x4=3
3x1+8x2-x3+x4=1
x1-9x2+3x3+7x4=7
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.1.参考答案-1
1 5 -1 -1 -1
1 -2 1 3 3
3 8 -1 1 1
1 -9 3 7 7
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1 5 -1 -1 -1
0 -7 2 4 4
0 -7 2 4 4
0-14 4 8 8
----
1 5 -1 -1 -1
0 -7 2 4 4
0 0 0 0 0
0 0 0 0 0
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1 5 -1 -1 -1
0 -7/2 1 2 2
0 0 0 0 0
0 0 0 0 0
-----
1 -3/2 0 1 1
0 -7/2 1 2 2
0 0 0 0 0
0 0 0 0 0
--
故有
x1=3/2x2-x4+1
x3=7/2x2-2x4+2