r3-r1-r2,r1-2r2,r3+r1
0 -7 7 8 11
1 2 0 -2 -4
0 7 -7 -8 3
0 -1 1 1 1
r1-7r4,r2+2r4,r3+7r4
0 0 0 1 4
1 0 2 0 -2
0 0 0 -1 10
0 -1 1 1 1
r3+r1,r4-r1
0 0 0 1 4
1 0 2 0 -2
0 0 0 0 14
0 -1 1 0 -3
依次:r3*(1/14),r1-4r3,r2+2r3,r4+3r3,r4*(-1)
0 0 0 1 0
1 0 2 0 0
0 0 0 0 1
0 1 -1 0 0
交换行得
1 0 2 0 0
0 1 -1 0 0
0 0 0 1 0
0 0 0 0 1
在做习题时注意方法.