`1, (x + 3)(x - 4) + (x - 4)^2`
`= x^2 - 4x + 3x - 12 + x^2 - 2.x. 4 + 4^2`
`= x^2 - 4x + 3x - 12 + x^2 - 8x + 16`
`= x^2 -9x + 4`
`2, (x - 2)^2 - (x - 5)^2`
`= (x - 2 - x + 5)(x - 2 + x - 5)`
`= 3(2x - 7)`
`= 6x - 21`
`3, (x + 2)(x^2 - 2x + 4) - (x^3 + 8)`
`= (x + 2)(x^2 - 2x + 2^2) - (x^3 + 2^3)`
`= (x^3 + 2^3) - (x^3 + 2^3)`
`= 0`