bonsoir
12) 3 x - 5 = 2 x + 9
3 x - 2 x = 9 + 5
x = 14
13) x + 3 = 2 x - 5
x - 2 x = - 5 - 3
- x = - 8 ⇔ x = 8
14) 8 x - 3 = 4 x + 9
8 x - 4 x = 9 + 3
4 x = 12
x = 3
15) 6 x - 4 = 5 x + 3
6 x - 5 x = 3 + 4
x = 7
16) x + 4 = 3 x - 6
x - 3 x = - 6 - 4
- 2 x = - 10
x = 5
17) 3 x - 6 + 5 x = 4 x + 2
8 x - 4 x = 2 + 6
4 x = 8
x = 8/4 = 2
18)( 2 x + 1 ) / 5 = ( 3 x - 2) / 3
6 x + 3 = 15 x - 10
6 x - 15 x = - 10 - 3
- 9 x = - 13
x = 13/9
19) 4 x /6 + 3/6 = (10 x - 4 ) / 6
4 x - 10 x = - 4 - 3
- 6 x = - 7
x = 7/6
idem pour le 20 , dénominateur commun = 6