利用初等行变换求下列矩阵的列向量组的一个最大无关组,并把其余列向量用最大无关组线性表示

(a1,a2,a3,a4,a5)=
1 1 2 2 1
0 2 1 5 -1
2 0 3 -1 3
1 1 0 4 -1
r3-2r1,r4-r1
1 1 2 2 1
0 2 1 5 -1
0 -2 -1 -5 1
0 0 -2 2 -2
r3+r2,r4*(-1/2)
1 1 2 2 1
0 2 1 5 -1
0 0 0 0 0
0 0 1 -1 1
r1-2r4,r2-r4
1 1 0 4 -1
0 2 0 6 -2
0 0 0 0 0
0 0 1 -1 1
r2*(1/2)
1 1 0 4 -1
0 1 0 3 -1
0 0 0 0 0
0 0 1 -1 1
r1-r2,r3r4
1 0 0 1 0
0 1 0 3 -1
0 0 1 -1 1
0 0 0 0 0
秩=3.
极大无关组:a1,a2,a3
a4 = a1+3a2-a3
a5 = -a2 +a3