9.5 1) ~a+ 4~b−5~c=
3
7
−4
−4 6
−5
5
2
=
3 + 4·(−4)−5·5 7 + 4·6−5·2
=
−38 21
2) −3~a+12~b−~c=−3
3
7
+12
−4 6
−
5
2
=
−3·3 + 12 ·(−4)−5
−3·7 + 12 ·6−2
=
−16
−20
3) 5~b−2~c= 5
−4 6
−2
5
2
=
5·(−4)−2·5 5·6−2·2
=
−30 26
Géométrie : bases Corrigé 9.5