Réponse :

Bonjour,

1) 2x + 5 / 4 = 3/7

2x+5 = 3*4 / 7

2x = 12/7 - 5/1

2x = 12 - 35 / 7

2x = -23 / 7

x = (-23/7) / 2

x = -23 / 7 * 1/2

x = -23 / 14

2) 1/ x-2 = 2 / x

x-2 = 1/2 * x

(on a inversé l'équation tout simplement)

x/2 - x/1 = -2

x/2 - 2x / 2 = -2

-x / 2 = -2

-x = -2*2

x = 4

3) 5-x / 4 = 3+x / 3

5/4 - x/4 = 3/3 + x/3

-x/4 -x/3 = 1 - 5/4

x(-1/4 - 1/3) = 4-5 / 4

x (-3/12 - 4/12) = -1/4

-7/12 * x = -1/4

x = (-1/4) * ((-12) / 7)

x = 12 / 28

x = 3*2*2 / 7*2 * 2

x = 3/7

Exercice 9:

1) 4.3 x - 5.7x = 33-12

-1.4 x = 21

x = 21/ -1.4

x = -15

2) -0.7x -2.3x = 0.9 - 4.9

-3x = -4

x = 4/3