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Meilleure réponse !
2014-05-11T13:29:14+02:00
A. 3+4=2+6
3x - 2x = 6 -4
 x = 2
b. 7+13=5+21
7x - 5x = 21 - 13
2x = 8
x = 8/2
x= 4
c.13+1=9+21
13x - 9x = 21 - 1
4x = 20
x = 20/4
x = 5

d. 13+11=7+29
13x - 7x = 29 - 11
6x =18
x = 18/6
x= 3