3)x³-(x³-3x)(x+3); 6)(x+y)(x-2)(x-1)(x-2)

Решение:

1. \(x^3-(x^3-3x)(x+3) = x^3 - (x^4 + 3x^3 - 3x^2 - 9x) = x^3 - x^4 - 3x^3 + 3x^2 + 9x = -x^4 - 2x^3 + 3x^2 + 9x\)
2. \((x+y)(x-2)^2(x-1) = (x+y)(x^2-4x+4)(x-1) = (x+y)(x^3 - x^2 - 4x^2 + 4x + 4x - 4) = (x+y)(x^3 - 5x^2 + 8x - 4) = x^4 - 5x^3 + 8x^2 - 4x + yx^3 - 5yx^2 + 8yx - 4y = x^4 + (y-5)x^3 + (8-5y)x^2 + (8y-4)x - 4y\)

Ответ: 1) \(-x^4 - 2x^3 + 3x^2 + 9x\); 2) \(x^4 + (y-5)x^3 + (8-5y)x^2 + (8y-4)x - 4y\)