11 Tester l'égalité 5 + 3 X x = 7 X x- 4 pour : a) x = 0,5 b) x = 2,5 c) x = 2,25.

5+3x = 7x-4

a) 5+3x = 7x-4

a) 5+3x = 7x-4 5+3×0,5 = 7×0,5-4

a) 5+3x = 7x-4 5+3×0,5 = 7×0,5-4 5+1,5 = 3,5-4

a) 5+3x = 7x-4 5+3×0,5 = 7×0,5-4 5+1,5 = 3,5-4 6,5 = -0,5

6,5+0,5=0

7=0

b) 5+3x = 7x-4

+3x = 7x-4 5+3×2,5 = 7×2,5-4

+3x = 7x-4 5+3×2,5 = 7×2,5-4 5+7,5 = 17,5-4

+3x = 7x-4 5+3×2,5 = 7×2,5-4 5+7,5 = 17,5-4 12,5 = 13,5

12,5-13,5 = 0

-1 = 0

c) 5+3x = 7x-4

5+3×2,25 = 7×2,25-4

5+6,25 = 15,75-4

11,25 = 11,75

11,25-11,75 = 0

-0,5 = 0