`a) 3x . (x-2) - x . (1 + 3x) = 14`
`<=> 3x^2 - 6x - x - 3x^2 = 14`
`<=> -7x = 14`
`<=> x = 14 :(-7)`
`<=> x = -2`
Vậy `x = -2`
`b) 2x . (x+3) - 3 . (x^2 + 1) = x + 1 - x . (x-2)`
`<=> 2x^2 + 6x - 3x^2 - 3 = x + 1 - x^2 + 2x`
`<=> 2x^2 - 3x^2 + x^2 + 6x - x - 2x = 1 + 3`
`<=> 3x = 4`
`<=> x = 4/3`
Vậy `x = 4/3`
`c) 4. (18 - 5x) - 12 . (3x - 7) = 15 . (2x-16) - 6.(x+14)`
`<=> 72 - 20x - 36x + 84 = 30x - 240 - 6x - 84`
`<=> -20x - 36x -30x + 6x = -240 - 84 - 72 - 84`
`<=> -80x = -480`
`<=> x = -480 : (-80)`
`<=> x = 6`
Vậy `x = 6`
`d) 2x . (3x+1) + (4-2x).3x = 7`
`<=> 6x^2 + 2x + 12x - 6x^2 = 7`
`<=> 14x = 7`
`<=> x = 7 : 14`
`<=> x = 1/2`
Vậy `x = 1/2`
