a) -2.(x + 6) + 6.(x + 10) = 8
-2x - 12 + 6x + 60 = 8
4x = 8 + 12 - 60
4x = -40
x = -10
Vậy x = -10
b) -4.(2x + 9) - (-8x + 3) - (x + 13) = 0
-8x - 36 + 8x - 3 - x - 13 = 0
-x = 36 + 3 + 13
-x = 52
x = -52
Vậy x = -52
c) 7x.(2 + x) - 7x.(x + 3) = 14
14x + 7x² - 7x² - 21x = 14
-7x = 14
x = -2
Vậy x = -2