Bài 2:
a) `(5x- 2) - (4x-4) = (3x+1) - (3x-2)`
`5x -2 - 4x +4 = 3x+1 - 3x +2`
` 5x - 4x -3x +3x = 1 +2 +2 -4`
`(5-4-3+3)x = 1`
`x = 1`
Vậy `x = 1`
b) `5(x-1) - 8(x+1) = -11`
`5x- 5 - 8x -8= -11`
`(5x- 8x) - (5+8) = -11`
` -3x - 13 = -11`
`-3x= -11 +13`
`-3x = 2`
`x= -2/3`
Vậy `x= -2/3`
Bài 3:
Ta có: `M(x) = 20x^2 + 40x + 1989`
`M(x) = 20x^2 + 40x - 4 + 1993`
`M(x) = 4(5x^2 + 10x -1) +1993`
`M(x) =4.7 + 1993`
`M(x) = 28 + 1993`
`M(x)=2021`
Vậy `M(x) = 2021`