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
