Réponse :

Bonjour,

Exercice 2

1) x-7.4 = 27.4

x = 27.4 + 7.4

x = 34.8

2) 5x = 39

x = 39/5 = 7.8

3) x = -32.3 + 24.6

x = -7.7

4) 4x = 67 - 39

4x =28

x = 28/4 = 7

5) 13x - 7x = 79 - 37

6 x = 42

x = 42/6 = 7

6)3x -7x = 7+5

-4x = 12

x = 12/-4

x = 3

7) Erreur dans l'énoncé.

8) 8x - 3x + 2x = 24 + 39 - 14

3x = 49

x = 49/3

9) 2x + 12 = 9x - 3x + 27

2x -6x = 27 - 12

-4x = 15

x = 15/-4

10) x/4 = 40

x/4 * 4 = 40*4

x = 160

11) x² = 81

x= √81 = 9

12) x² - 2x - 15 = 0

Fonction polynôme sous la forme ax² + bx + c = 0

Où a = 1, b = -2 et c = -15

Δ = b² - 4ac  = (-2)² - 4 * 1 * (-15)

= 4 - (-60) = 4+60=64. Et √Δ = √64 = 8.

Comme Δ > 0.   Deux solutions:

x1 = (-b - √Δ) / 2a = (2 - 8) / 2 = -6 /2 = -3

x2 = (-b+ √Δ) / 2a = (2+8) / 2 = 10/2 = 5.

donc S = {-3;5}

x2 = (-b + √Δ) / 2a