`a) x^2(x-2x^3) = x^3 - 2x^5`
`b) (x+1)(5-x) = 5x + 5 -x^2 - x = - x^2 + 4x + 5`
`c) (x-2)(x^2 + 3x - 4) = x^3 + 3x^2- 4x - 2x^2 - 6x + 8 = x^3 + x^2 - 10x + 8`
`d) ( x - 2)(x - x^2 + 4 ) = x^2 - x^3 + 4x - 2x + 2x^2 - 8 = -x^3 + 3x^2 + 2x - 8`
`e) (x^2 - 1)(x^2 + 2x) = x^4 + 2x^3 - x^2 - 2x`
`f) (2x-1)(3x+2)(2-x) = (2x-1)(6x - 3x^2 + 4 - 2x) = (2x-1)(-3x^2 + 4x + 4 ) = -6x^3 + 8x^2 + 8x + 3x^2 - 4x - 4 = -6x^3 + 11x^2 + 4x - 4`