Sagot :
Exercice 1 :
méthode 1 méthode 2 :
a. 4x = 12 a. 4x = 12
x = 12/4 4x/4 = 12/4
x = 3 x = 3
b. x - 3 = 2 b. x - 3 = 2
x = 2 + 3 x - 3 + 3 = 2 + 3
x = 5 x = 5
c. 2x + 1 = 17 c. 2x + 1 = 17
2x = 17 - 1 2x + 1 - 1 = 17 - 1
2x = 16 2x = 16
x = 16/2 2x/2 = 16/2
x = 8 x = 8
d) 2 - 5x = x d. 2 - 5x = x
2 = x + 5x 2 - 5x +5x = x + 5x
2 = 6x 2 = 6x
x = 2/6 x = 2/6
x = 1/3 x = 1/3
e) 5x + 7 = 3x - 19 e. 5x + 7 = 3x - 19
5x - 3x = - 19 - 7 e. 5x + 7 - 7 = 3x - 19 - 7
2x = - 26 �� 5x = 3x - 26
x = - 26/2 5x - 3x = 3x - 26 - 3x
x = - 13 2x = -26
x = - 26/2 ⇒ x = - 13
f) 6x - 9 = 4(2 – 3x) 6x - 9 = 4(2 – 3x)
6x - 9 = 8 - 12x 6x - 9 = 8 - 12x
6x + 12x = 8 + 9 6x - 9 + 9 = 8 - 12x + 9
18x = 17 6x = - 12x + 17
x = 17/18 6x + 12x = - 12x + 12x + 17
18x = 17 ⇒ x = 17/18
Exercice 2 :
Soit x le prix d'un stylo
a. 4 stylos = 4x
b. 2 stylos = 2x
c. 1 compas = 5x
2. 4x + 2x + 5x = 13,75
3. 4x + 2x + 5x = 13,75
11x = 13,75
x = 13,75/11
x = 1,25
Le prix d'un stylo est donc de 1,25€