(a1,a2,a3,b)=
1 1 -2 3
2 1 -6 4
3 2 -7 7
r3-r1-r2,r2-2r1
1 1 -2 3
0 -1 -2 -2
0 0 1 0
r1+2r3,r2+2r3
1 1 0 3
0 -1 0 -2
0 0 1 0
r1+r2,r2*(-1)
1 0 0 1
0 1 0 2
0 0 1 0
所以 r(a1,a2,a3)=3
所以 a1,a2,a3 是R^3的基,且b=a1+2a2
(a1,a2,a3,b)=
1 1 -2 3
2 1 -6 4
3 2 -7 7
r3-r1-r2,r2-2r1
1 1 -2 3
0 -1 -2 -2
0 0 1 0
r1+2r3,r2+2r3
1 1 0 3
0 -1 0 -2
0 0 1 0
r1+r2,r2*(-1)
1 0 0 1
0 1 0 2
0 0 1 0
所以 r(a1,a2,a3)=3
所以 a1,a2,a3 是R^3的基,且b=a1+2a2