Bonjour !
1.
3x + 7 = x - 1
3x + 7 - x = x - 1 - x
2x + 7 = -1
2x + 7 - 7 = -1 - 7
2x = -8
2x/2 = -8/2
x = -4
2.
6 - x = x + 14
6 - x + x = x + 14 + x
6 = 2x + 14
6 - 14 = 2x + 14 - 14
-8 = 2x
2x/2 = -8/2
x = -4
3.
3(x + 7) = 4x + 9
3*x + 3*7 = 4x + 9
3x + 21 = 4x + 9
3x + 21 - 3x = 4x + 9 - 3x
21 = x + 9
21 - 9 = x + 9 - 9
12 = x
x = 12
4.
2(x - 4) = 7x - 2
2*x - 4*2 = 7x - 2
2x - 8 = 7x - 2
2x - 8 - 2x = 7x - 2 - 2x
-8 = 5x - 2
-8 + 2 = 5x - 2 + 2
-6 = 5x
5x/5 = -6/5
x = -1,2
J'espère t'avoir aidé. Bon courage !
