Bonsoir,
6x-9 =12 -3x
6x+3x = 12+9
9x = 21
x= 21/9 = 7/3= 2,3333
a)
2x+x = 4+3
3x = 7
x= 7/3
oui
b)
2x+x = 6+3
3x = 9
x= 9/3 = 3
non
c)
9x = 21
x= 21/9 = 7/3
oui
d)
9x = 12+9
9x = 21
x= 21/9 = 7/2
oui
5x-2 = -7
5x= -7+2
5x = -5
x= -5/5 = -1
9x = 64 -1
9x = 63
x= 63/9 = 7
je te laisse vérifier