Thực hiện phép tính -)

`3) (x+2)^2 - (x-3)(x+1)`

`= (x^2 + 4x + 4) - (x^2 + x - 3x - 3)`

`= x^2 + 4x + 4 - (x^2 - 2x - 3)`

`= x^2 + 4x + 4 - x^2 + 2x + 3`

`= 6x + 7`

`5) (x-2)^2 + (x-1)(x+5)`

`= (x^2 - 4x + 4) + (x^2 + 5x - x - 5)`

`= x^2 - 4x + 4 + x^2 + 4x - 5`

`= 2x^2 - 1`

`7) (1-2x)(5-3x) + (4-x)^2`

`= (5 - 3x - 10x + 6x^2) + (16 - 8x + x^2)`

`= 6x^2 - 13x + 5 + x^2 - 8x + 16`

`= 7x^2 - 21x + 21`

`9) (x+1)^2 + (x-2)(x+2) - 4x`

`= (x^2 + 2x + 1) + (x^2 - 4) - 4x`

`= x^2 + 2x + 1 + x^2 - 4 - 4x`

`= 2x^2 - 2x - 3`

`11) (x+4)^2 + (x+5)(x-5) - 2x(x+1)`

`= (x^2 + 8x + 16) + (x^2 - 25) - (2x^2 + 2x)`

`= x^2 + 8x + 16 + x^2 - 25 - 2x^2 - 2x`

`= (x^2 + x^2 - 2x^2) + (8x - 2x) + (16 - 25)`

`= 6x - 9`

`13) (x-1)^2 - 2(x+3)(x-3) + 4x(x-4)`

`= (x^2 - 2x + 1) - 2(x^2 - 9) + (4x^2 - 16x)`

`= x^2 - 2x + 1 - 2x^2 + 18 + 4x^2 - 16x`

`= (x^2 - 2x^2 + 4x^2) + (-2x - 16x) + (1 + 18)`

`= 3x^2 - 18x + 19`