Sagot :
bonjour
x + 3 = 12
x = 12 - 3
x = 9
- 3 x + 17 = 21 - x
- 3 x + x = 21 - 17
- 2 x = 4
x = - 2
3 x - 3 = 4 x - 4
3 x - 4 x = - 4 +3
- x = - 1
x = 1
15 + 7 x = 2 x
7 x - 2 x = - 15
5 x = - 15
x = - 3
2 x+ 8 = 6 x
2 x - 6 x = - 8
- 4 x = - 8
x = 2
15 x + 27 = 28 + 20 x
15 x - 20 x = 28 - 27
- 5 x = 1
x = - 1/5