7.5 1) ~v+ 2v~2−5v~1 =~0
~v =−2v~2+ 5v~1
=−2 −1 4
!
+ 5 −2 3
!
= −2·(−1) + 5·(−2)
−2·4 + 5·3
!
= −8 7
!
2) −3~v
−v~3 = 12v~3
−v~1
−3~v = 32v~3 −v~1
~v =−
1
2v~3+13v~1
=−
1 2
3 4
!
+13 −2 3
!
= −
1
2 ·3 + 13 ·(−2)
−
1
2 ·4 + 13 ·3
!
= −
13 6
−1
!
3) 53~v+32v~4 =v~3−2v~2
5
3~v =v~3−2v~2−
3 2v~4
~v = 35v~3
−
6 5v~2
−
9 10v~4
= 35
3 4
!
−
6 5
−1 4
!
−
9 10
4 0
!
=
3 5 ·3−
6
5 ·(−1)−
9 10 ·4
3 5 ·4−
6 5 ·4−
9 10 ·0
!
= −
3 5
−
12 5
!
Géométrie : bases Corrigé 7.5