Bonjour,
Exercice 71 :
a) 4AD - 4BD + 2CD = 0
4AD -4BA - 4AD + 2CD = 0
-4BA = -2CD
2BA = CD
b) CB+2AC+DB=0
AC+CB+AC+DB=0
AB+AC+DB=0
AB+AB+BC+DB=0
2AB+DB+BC=0
2AB+DC=0
AB=-1/2 DC
c) 5AB -3CB = 7AD - 4AC
2AB +3(AB-CB)= 7AD - 4AC
2AB + 3(AB+BC) = 7AD - 4AC
2AB +3AC = 7AD -4AC
2AB +3AC +4AC - 7AD=0
2AB +7(AC-AD)=0
2AB +7(AC+DA)=0
2AB +7DC=0
2AB = -7DC
2AB = 7CD
AB=7/2 CD
Il faut ensuite rajouter les vecteurs au dessus
