Sagot :
Bonjour,
a. - 2x + 7 = -x + 9
7-9 = -x +2x
-2 = x
x= -2
b. 4x - 21 = 7x – 9
-21+9 = 7x -4x
-12 = 3x
3x = -12
x = -12/3
x= -4
d.-7x - 12 = 8x + 3
-12 -3 =8x+7x
-15 = 15x
15x= -15
x= -15/15
x= -1
d. 7x + 13 = -3x - 7
7x+3x = -7 -13
10x = -20
x = -20/10
x = - 2