Bonjour,

a.

2 * x - 1 = 7

2x - 1 = 7

2x = 7 + 1

2x = 8

x = 8/2

x = 4

2 * 4 - 1 = 7

8 - 1 = 7

7 = 7 --> Oui

b.

4 * (5 + 2) = 40

4 * 10 = 40

40 = 40 --> Oui.

c.

5 * n - 4 = 5n - 4 --> Non.