Réponse:

1. 4- 5 = - 1

- 1 x 4 = - 4

2. (- 3)^2 = 9

9 - 4 = 5

3. (x- 5) x x = x^2 - 5x

4. x^2 - 4

5. x^2 - 5x = x^2 - 4

x^2 - 5x - x^2 = x^2 - 4 - x^2

- 5x = - 4

x = 4/5