bonjour

3 x + 7 = 0

3 x = - 7

x = - 7 /3

6 - x = 4

- x = 4 - 6

- x = - 2

x = - 2

3 x + 21 = 9

3 x = 9 - 21

3 x = - 12

x = - 4

x - 8 = 0

x = 8

3 x + 7 = x - 1

3 x - x = - 1 - 7

2 x = - 8

x = - 4

3 x + 21 = 4 x + 9

3 x - 4 x = 9 - 21

- x = - 12

x = 12

6 - x = x + 14

- x + x = 14 - 6

0 x = 8  donc pas de solution  

2 x - 8 = 7 x - 2

2 x - 7 x = - 2 + 8

- 5 x = 6

x = - 6/5